THE  SCIENCE 
OF  EVERYDAY  LIFE 

PROJECTS  FOR  JUNIOR  HIGH  SCHOOLS 


EDGAR  F.VANBUSKIRK,A.M. 

Assistant  Educational  Director,  United  States  Public  Health 

Service ;  Director,  Work  in  General  Science,  DeWitt  Clinton 

High  School,  New  York  City 


AND 


EDITH  LILLIAN  SMITH,  A.B. 

Instructor,  Boston  Normal  School  j  Special  Teacher  of  General 
Science  in  the  Model  School 


HOUGHTON  MIFFLIN  COMPANY 

BOSTON     NEW  YORK     CHICAGO 

Iiitier0i&e  prc?£  Cambridge 


COPYRIGHT,   1919,  BY  EDITH   LILLIAN    SMITH    AND   EDGAR   F.    VAN   PUSKIRK 


ALL  RIGHTS  RESERVED 


Cl)t  fcibcrstlie  $res$ 

CAMBRIDGE  .  MASSACHUSETTS 
U  .  S  .  A 


INTRODUCTION 

BY  THOMAS  H.  BRIGGS,  PH.D. 

Associate  Professor  of  Education,  Department  of  Secondary  Education, 
Teachers  College,  Columbia  University 

THAT  education  during  the  intermediate  school  period  has  been 
unsatisfactory  is  proved  not  so  much  by  the  number  of  criticisms 
directed  against  it  as  by  the  general  willingness  of  schoolmen  to 
modify  their  programs.  To  make  satisfactory  changes  in  the 
curricula  and  courses  of  study,  there  is  need  of  a  convincing 
statement  of  worthy  purposes  for  the  school,  and  of  definite  but 
non-restricting  outlines  of  courses  for  the  several  subjects. 

The  chief  educational  purpose  of  the  junior  high  school  is  con- 
ceived as  the  exploration,  by  means  of  subject-matter  in  itself 
worth  while,  of  the  interests,  aptitudes,  and  capacities  of  the 
pupils,  and  at  the  same  time  for  the  pupils  of  the  possibilities  in 
the  major  fields  of  learning  and  activity.  An  acceptance  of  this 
statement  of  purpose  carries  with  it  the  obligation  to  furnish 
education  that  is  of  the  maximum  value  even  if  a  pupil  should 
drop  out  of  school  at  the  end  of  any  term  or  month  or  week ;  to 
learn  through  the  studies  the  particular  needs,  interests,  apti- 
tudes, and  capacities  of  each  pupil,  so  that  he  may  be  most  wisely 
advised  in  regard  to  his  future;  and  to  reveal  to  him  the  impor- 
tance and  the  limitations  of  the  several  major  fields  of  learning 
and  of  activity,  so  that  he  may  intelligently  participate  in  de- 
termining his  own  future. 

The  worth  of  proposed  details  in  any  subject  of  study  may  be 
judged  by  the  extent  to  which  they  agree  with  two  other  state- 
ments of  general  purpose :  The  first  duty  of  the  school  is  to  train 
its  pupils  to  perform  better  the  desirable  activities  that  they  are 
most  likely  to  perform  anyway.  A  second  duty  is  to  reveal 
higher  types  of  activity  and  to  make  them  both  desired  and  to  an 


iv  INTRODUCTION 

extent  possible.  In  selecting  details,  then,  it  becomes  necessary  to 
ask  what  desirable  activities  the  pupils  are  most  likely  to  per- 
form outside  the  classroom,  and  in  what  ways  any  particular  sub- 
ject of  study  can  lead  to  a  better  performance  of  them. 

A  careful  and  continued  inventory  shows  that  the  adult  who 
has  not  by  further  study  become  a  specialist  needs  training  in 
science  for  four  purposes,  here  enumerated  in  the  order  of  their 
importance  for  the  average  person:  first,  to  understand  and  ap- 
preciate the  physical  phenomena  most  common  in  his  life;  second, 
to  perform  more  intelligently  practical  tasks  in  the  home  or  in  a 
vocation;  third,  to  know  somewhat  definitely  where  he  may  find 
information  regarding  scientific  facts  and  what  general  applica- 
tions the  several  sciences  have  in  the  world;  and  fourth,  to  pre- 
pare him  for  future  advancement,  either  in  the  study  of  pure 
science  or  in  practical  applications  demanded  by  the  vocation 
elected. 

First  of  all,  courses  in  science  should  afford  culture.  All  men 
and  women  are  most  of  the  time  consumers  rather  than  producers; 
hence  it  is  wise  that  as  early  as  possible  with  economy  every  one 
should  be  given  an  intelligent  understanding  of  the  most  common 
phenomena  in  the  environing  universe.  This  intelligent  under- 
standing is  not  necessarily  exhaustive;  it  is  such  that  it  satisfies 
the  intellectual  demand  to  know  what  various  common  objects 
are,  how  they  work,  what  they  are  for,  and  how  they  are  caused. 
Most  of  this  desired  information  is  too  incomplete  to  insure  pro- 
duction ;  but  it  is  a  desirable,  perhaps  a  necessary,  preparation  for 
the  later  acquisition  of  the  more  detailed  and  accurate  study,  it 
satisfies  the  very  actual  social  needs,  thus  making  us  more  com- 
fortable as  participating  in  the  knowledge  common  to  our  fellows, 
and  it  increases  appreciation  of  the  commonest  and  most  strik- 
ing phenomena  in  our  lives.  The  possession  of  such  knowledge 
surely  should  provide  enduring  satisfaction  and  abiding  interest 
in  the  world  of  science. 

Second,  courses  in  science  should  train  pupils  to  do,  with  intel- 
ligent understanding  and  economy,  such  tasks  as  are  most  likely 
to  be  theirs  in  life.  This  is  frankly  a  demand  for  the  emphasis  to 
be  placed  on  specific  rather  than  on  general  habits.  Whatever 


INTRODUCTION  v 

our  belief  concerning  general  habits,  we  can  hardly  deny  that  de- 
sirable general  habits  can  be  secured  only  after  and  by  means  of 
desirable  specific  habits.  '  By  making  the  latter  our  primary  in- 
terest, we  shall  at  least  have  some  valuable  and  practical  results 
from  the  science  instruction,  whether  "the  scientific  attitude  of 
the  mind"  and  other  such  larger  ends  are  attained  or  not. 

Third,  courses  in  science  should  explore  both  the  field  of  sci- 
ence and  the  pupil  himself.  The  generally  prevalent  elective 
system  in  secondary  and  higher  education  is  based  on  the  assump- 
tion .that  the  elector  knows  his  own  aptitudes,  interests,  and  abili- 
ties, and  that  he  understands  something  of  the  subjects  —  their 
content  and  their  methods  —  among  which  he  must  choose. 
Such  valuable  information  could  certainly  be  imparted  economi- 
cally and  effectively  in  courses  in  general  science.  If  the  student 
can  be  shown  during  an  introductory  survey  course  that  science 
is  of  assured  value  to  him,  the  election  of  other  advanced  science 
studies  will  be  more  nearly  what  was  generally  prophesied  when 
the  subjects,  less  than  a  generation  ago,  were  given  their  present 
emphasis. 

Fourth  and  finally,  courses  in  general  science  should  prepare 
pupils  for  the  higher  study  of  such  science  as  they  may  afterward 
elect. 

Surely  the  success  of  the  introductory  work  is  very  largely 
measurable  by  the  interests  aroused;  in  fact,  if  it  should  come 
to  a  choice  between  receiving  pupils  full  of  a  substantial  enthu- 
siasm but  with  little  organized  knowledge,  and  receiving  pupils 
possessing  a  well-organized  body  of  principles  but  predisposed 
against  a  continuance  of  the  subject,  few  teachers  of  advanced 
science  would  hesitate.  Fortunately,  neither  extreme  is  neces- 
sary ;  every  teacher  of  the  intermediate  schools  will  attempt  to 
give  the  pupils  principles  supported  by  abundant  facts  common 
in  every  one's  experience,  but  if  his  work  is  to  be  most  effec- 
tive, he  must  at  the  same  time  insure  interest  in  science  and  an 
eager  desire  for  more  of  it. 

The  Science  of  Everyday  Life  attempts  to  translate  these  prin- 
ciples into  an  introductory  course  for  pupils  from  twelve  to 
sixteen  years  of  age.  Abandoning  the  vertical  stratifications 


VI 


INTRODUCTION 


between  subjects,  artificial  distinctions  observed  nowhere  by 
practical  men  of  the  world  or  by  scientists  in  research  or  in  busi- 
ness it  presents  information  about  a  large  number  of  physical 
phenomena  that  the  authors  consider  most  important  for  boys 
and  girls,  whether  they  continue  in  school  or  drop  out  to  enter  the 
several  vocations.  To  avoid  economic  aimlessness,  it  organizes 
the  details  under  the  five  major  topics  of  Air,  Water,  Food,  Pro- 
tection, and  the  Work  of  the  World,  presenting  under  them  a 
series  of  projects.  Each  of  these,  which  it  attempts  to  present 
as  worth  while  to  the  pupil,  leads  to  general  principles  that  surely 
should  be  understood  by  every  intelligent  man  or  woman. 

Every  effort  has  been  expended  to  make  the  book  teachable, 
attention  being  paid  especially  to  the  arousing  of  interest,  the 
stimulus  to  initiative,  the  economy  of  time,  the  laws  of  learning, 
the  correlation  with  other  subjects,  and  the  varied  needs  because 
of  individual  differences  in  ability,  in  interests,  and  in  particular 
aptitudes.  The  problems  proposed  and  the  annotated  bibliog- 
raphies presented  at  the  end  of  each  chapter  should  be  of  par- 
ticular value  to  the  teacher  who  desires  to  extend  the  work  on 
any  of  the  topics. 


CONTENTS 


PART  I.  THE  CHIEF  NECESSITIES  OF  LIFE 
INTRODUCTION  . 


UNIT  I.   THE  AIR  AND  HOW  WE  USE  IT 

PROJECT  I.  THE  AIR  A  REAL  SUBSTANCE 

INTRODUCTION 3 

Air  is  real. 

PROBLEMS 4 

TOPICS: 

Three  forms  of  matter,  8.  The  atmosphere  an  ocean  of  air,  9.  Air 
pressure,  10.  Making  a  mercurial  barometer,  10.  The  barometer  used 
to  indicate  height,  10.  The  aneroid  barometer,  n.  The  barometer 
used  to  forecast  weather,  12.  Air  pressure  and  the  suction  pump,  12. 
The  force  pump,  12.  Air  pressure  and  the  exhaust  pump,  12.  The 
bicycle  pump,  13.  Air  pressure  and  the  action  of  the  siphon,  13.  Pres- 
sure on  the  human  body,  13.  Structure  of  the  human  ear,  14.  Air  trans- 
mits sound,  15.  The  nature  of  sound,  16.  The  rate  at  which  sound 
travels,  16.  Compressed  air,  17.  Liquid  air,  17.  Balloons,  18.  Air- 
planes, 19. 

INDIVIDUAL  PROJECTS 20 

PROJECT  II.  AIR  AND  FIRE 

INTRODUCTION      ....'.      .      .      .      .      .      .      .      .      .      .21 

Fire  in  its  relation  to  our  lives. 

PROBLEMS         .      .,     .      ,      ,      .      * -.;'*-.     .      .    ..      ...    22 

TOPICS: 

A  fire  needs  air,  26.  Composition  of  the  air,  26.  Burning  decreases 
the  amount  of  oxygen,  27.  Extinguishing  fires,  27.  Burning  often  in- 
creases the  amount  of  carbon  dioxide  and  water  in  the  air,  27.  Ele- 
ments and  compounds,  28.  Compounds  are  different  from  the  ele- 
ments composing  them,  28.  Elements  may  combine  with  each  other, 
29.  Oxidation,  30.  Kinds  of  oxidation,  30.  Slow  oxidation,  30.  Ox- 


viii  CONTENTS    • 

idation  helps  us  work,  31.  Matches,  31.  Matter  may  change  its  form 
but  cannot  be  destroyed,  32.  Matter  cannot  be  created,  33. 

INDIVIDUAL  PROJECTS 33 

PROJECT  III.  AIR  AND  BREATHING 

INTRODUCTION         34 

All  plants  and  animals  breathe. 

PROBLEMS         34 

TOPICS: 

Activity  in  relation  to  the  rate  of  breathing,  40.  Heat  production  in  re- 
lation to  the  rate  of  breathing,  40.  Air  that  we  breathe  in,  41 .  Air  that 
we  breathe  out,  41.  Breathing  of  plants,  42.  The  human  body  a  ma- 
chine, 42.  Cells,  the  building  units  of  the  living  body,  42.  Parts  of  a 
cell,  43.  How  many  cells  a  living  body  contains,  43.  Tissues  and  or- 
gans, 44.  Cells  in  the  blood,  44.  The  breathing  organs  of  the  human 
body,  45.  Why  the  air  passes  into  and  out  of  the  lungs,  45.  The  value 
of  deep  breathing,  46.  Oxidation  in  the  cells  of  the  body,  46.  What  be- 
comes of  the  waste  matter,  46.  Artificial  respiration,  47. 

INDIVIDUAL  PROJECTS 48 

PROJECT  IV.  AIR  AND  HEALTH 


INTRODUCTION 50 

Fresh  air. 

PROBLEMS 51 

TOPICS: 

Factors  which  control  ventilation,  54.  Temperature  of  air,  54. 
Amount  of  water  vapor  in  the  air,  54.  Foreign  material  in  the  air,  55. 
Cleaning  and  dusting,  55.  Air  and  disease,  56.  Enemies  of  health,  56. 
How  bacteria  enter  the  body,  57.  How  bacteria  attack  the  body,  57. 
How  bacteria  increase  in  numbers,  58.  How  the  body  defends  itself 
against  the  attacks  of  bacteria,  58.  The  external  defenses,  59.  The 
internal  defenses,  59.  The  antitoxin  treatment  for  diphtheria,  60. 
Bacteria  present  in  healthy  people,  61.  Importance  of  keeping  the 
body  in  a  healthy  condition,  61.  How  to  keep  well,  62.  Effects  of 
alcohol  and  tobacco,  62.  Seasons  in  relation  to  prevalence  of  disease, 
63.  Some  ways  in  which  bacteria  are  spread,  63.  How  to  care  for 
the  sick,  65.  Antiseptics  and  germicides,  65.  What  the  community 
can  do  to  prevent  illness,  66. 

INDIVIDUAL  PROJECTS 66 


CONTENTS  ix 

UNIT  II.   WATER  AND  HOW  WE  USE  IT 
PROJECT  V.  WATER  IN  OUR  HOUSES 

INTRODUCTION 68 

Water  a  necessity  of  life. 
The  human  body  needs  water. 

PROBLEMS 70 

TOPICS: 

Sources  of  our  drinking-water,  78.  Pure  water  and  impure,  79.  Ty- 
phoid fever,  a  disease  often  spread  by  impure  drinking-water,  79. 
How  water  is  purified,  80.  Water  pressure,  82.  Water  supply  sys- 
tems, 83.  A  house  piping  system,  86.  A  hot-water  heater,  86. 
Waste  pipes  of  the  house,  87.  Sewage  disposal,  88.  Water  changes 
from  one  form  to  another:  the  physical  states,  89.  Water  freezes  to 
ice,  89.  Water  changes  to  vapor,  90.  Water  changes  to  steam,  90. 
Cooking  food  by  boiling,  90.  Changes  produced  in  food  by  boiling,  91. 
Water  as  a  solvent,  92.  Hard  and  soft  water,  93. 

INDIVIDUAL  PROJECTS 93 

PROJECT  VI.  WATER  IN  THE  AIR 

INTRODUCTION 96 

The  weather. 

PROBLEMS 97 

TOPICS: 

Water  in  an  invisible  form  in  the  air,  105.  How  the  water  vapor  gets 
into  the  air,  105.  Where  the  water  vapor  comes  from,  106.  Evapora- 
tion from  plants,  106.  The  thermometer,  106.  Temperature  and  the 
amount  of  water  vapor  in  the  air,  108.  Humidity  of  the  air,  108.  Con- 
densation, 109.  Kinds  of  clouds,  109.  Thunderstorms,  109.  Dew 
and  its  formation,  no.  The  wind,  no.  Winds  of  the  world,  112. 
Foretelling  a  storm,  113.  The  path  of  storms,  115.  The  Weather 
Bureau,  115.  The  value  of  rain,  116. 

INDIVIDUAL  PROJECTS   .      .      .      .      .      .      .      .      .      .      .      .117 

41 
PROJECT  VII.  WATER  AND  THE  SOIL 

INTRODUCTION 119 

How  soil  is  made. 

The  value  of  water  in  the  soil. 


x  CONTENTS 

PROBLEMS         .  121 

TOPICS: 

What  soil  contains,  125.  Rocks,  125.  Igneous  rocks,  125.  Sedimentary 
rocks,  126.  Metamorphic  rocks,  127.  The  action  of  water  in  making 
soil,  127.  The  action  of  ice,  130.  The  action  of  wind,  131.  The  action 
of  air,  131.  The  action  of  plants,  132.  The  action  of  animals,  132. 
Plants  need  water,  133.  Water  in  the  soil,  133.  How  water  rises  in 
the  soil,  134.  How  to  save  the  moisture  in  the  soil,  135.  Variation  in 
the  amount  of  rainfall,  136.  Reclaiming  desert  regions,  136.  Air  in 
the  soil,  137.  Reclaiming  swampy  regions,  137.  Acid  soil  and  how  to 
correct  it,  138. 

INDIVIDUAL  PROJECTS 138 

UNIT  III.  FOODS  AND  HOW  WE  USE  THEM 

PROJECT  VIII.  PLANTS  —  FOOD-MAKERS  FOR  THE 
WORLD 

INTRODUCTION 141 

Foods  —  a  necessity  of  life. 
Food  conservation. 

PROBLEMS 142 

TOPICS: 

Where  our  foods  come  from,  152.  Organic  and  inorganic  foods,  152. 
The  nutrients,  153.  Physical  and  chemical  changes,  153.  Where  do 
plants  get  their  food?  154.  The  organs  of  a  plant,  154.  Root-hairs, 
155.  How  a  root-hair  absorbs  soil  water,  155.  How  water  passes 
through  a  plant,  156.  Where  foods  are  manufactured,  157.  The  raw 
materials  needed,  157.  Starch  is  made  only  in  green  plants,  158.  The 
sun  furnishes  the  necessary  energy,  159.  The  waste  product  is  oxygen, 
159.  Leaves  make  all  the  organic  nutrients,  159.  Helping  plants  make 
foods,  159.  Nitrogen-fixing  bacteria,  160.  Electricity  as  a  means  of 
taking  nitrogen  out  of  the  air,  161.  Home  gardens,  161. 

INDIVIDUAL  PROJECTS 161 

PROJECT  IX.  FOODS  AND  THE  HUMAN  BODY 

INTRODUCTION 164 

The  two  great  uses  of  foods. 
PROBLEMS 164 

TOPICS: 

How  to  select  foods,  167.  The  amount  of  nourishment  in  foods,  167. 
Meaning  of  the  term  "  Calorie,"  168.  A  mixed  diet  usually  desirable,  168. 
People  need  varying  amounts  and  kinds  of  food,  169.  A  food  table,  1 70. 


CONTENTS  xi 

Food  charts,  172.  The  cost  of  foods,  179.  Taste  and  digestibility,  179. 
Quality  and  cleanliness,  179.  Tea,  coffee,  and  other  food  adjuncts,  180. 
Why  we  cook  foods,  180.  The  value  of  some  uncooked  foods,  180.  The 
food  tube,  1 80.  Digestion  and  its  use,  181.  Digestion  in  the  mouth, 
182.  Stomach  and  intestinal  digestion,  182.  The  circulation  of  blood, 
182.  Kinds  of  blood  vessels,  183.  Treatment  of  cuts,  183.  Stomach- 
aches, 184.  Headaches,  184.  Teeth  and  their  care,  184.  Structure 
of  a  tooth,  185.  Cavities  in  teeth,  185.  How  to  care  for  the  teeth,  186. 
The  effects  of  alcohol  and  tobacco  upon  digestion  and  circulation,  186. 

INDIVIDUAL  PROJECTS 187 

PROJECT  X.  FOODS  IN  THE  HOME 

INTRODUCTION 188 

Clean  foods. 

PROBLEMS         189 

TOPICS: 

Why  foods  spoil,  196.  Comparison  of  bacteria,  molds,  and  yeasts,  196. 
The  action  of  bacteria  on  food,  196.  The  action  of  molds  on  food,  197. 
How  to  avoid  molds,  197.  The  action  of  yeast  on  food,  198.  Yeast  as 
a  foe,  199.  Yeast  as  a  friend  —  breadmaking,  199.  How  to  protect 
foods  against  molds,  and  harmful  bacteria  and  yeasts,  199.  The  cold 
pack  method  of  canning,  200.  Drying  foods,  201.  Pure  milk,  201. 
Pasteurized  milk,  202.  Cuts  of  meat,  203.  Dangers  in  meat,  204. 
Cleanliness  in  the  kitchen,  204.  The  work  of  a  city  health  depart- 
ment, 205.  Pure  food  and  drug  laws,  205. 

INDIVIDUAL  PROJECTS 206 

PART  II.  MAN'S  CONTROL  OF  THE  FORCES  OF  NATURE 
INTRODUCTION  —  THE  FORCES  OF  NATURE 

Law  of  cause  and  effect,  208.  Early  explanations  of  natural  phe- 
nomena, 208.  Man's  control  of  the  forces  of  nature,  209.  Mat- 
ter and  energy,  209.  The  energy  of  living  beings,  211.  Energy  pos- 
sessed by  inanimate  objects,  211.  The  energy  of  motion  —  kinetic 
energy,  212.  Stored-up  energy  —  potential  energy,  212.  Forms  of  en- 
ergy, 213.  Energy  may  change  its  form,  213.  Energy  can  never  be 
made  from  nothing,  214.  Energy  cannot  be  destroyed,  214.  Some 
common  sources  of  energy,  214.  Conserving  nature's  storehouse  of  en- 
ergy, 215.  Original  source  of  all  energy  upon  the  earth,"2 15.  The  sun 
and  other  stars,  216.  Constellations,  216.  The  north  star,  217.  The 
solar  system,  217.  Moons,  219.  Years,  219.  Seasons,  219.  Day  and 
night,  220.  Time,  221.  Gravitation,  221. 

INDIVIDUAL  PROJECTS 223 


xii  CONTENTS 

UNIT  IV.   PROTECTION  — HOMES  AND  CLOTHING 
PROJECT  XI.  BUILDING  OUR  HOMES 

INTRODUCTION 225 

Homes  in  different  parts  of  the  world. 
Your  home. 

PROBLEMS 225 

TOPICS: 

Choosing  a  home,  234.  A  convenient  house,  234.  A  safe  house,  236. 
How  a  house  is  built  —  the  foundation,  237.  The  house  walls,  238. 
The  floors,  238.  The  roof,  239.  Materials  used  in  building  our  houses, 
239.  Wood  as  a  building  material,  239.  The  grain  of  wood,  239.  Hard 
woods  and  soft  woods,  240.  Why  wood  differs  in  value,  241.  Relative 
durability  of  common  woods,  241.  A  brick  house,  242.  Concrete  con- 
struction, 243.  A  house  of  stucco,  244.  Building  stones,  244. 

INDIVIDUAL  PROJECTS 245 

PROJECT  XII.  LIGHTING  OUR  HOMES 

INTRODUCTION 248 

A  well-lighted  house. 
Some  questions  to  answer. 

PROBLEMS 248 

TOPICS: 

How  our  houses  are  lighted  by  the  sun,  256.  Reflected  light,  256. 
Reflection  from  mirrors,  257.  Diffused  light,  257.  Refracted  light,  258. 
The  colors  in  sunlight,  259.  Why  anything  has  color,  259.  A  lens,  259. 
A  camera,  260.  The  human  eye,  261.  The  intensity  of  light,  262.  Nat- 
ural and  artificial  lighting,  262.  Candle  light,  262.  A  kerosene  lamp, 
263.  Gas  lighting,  263.  Electric  lights,  265.  Electric  cells,  266.  Con- 
ductors and  insulators,  267.  Switches,  267.  Fuses,  267.  An  incan- 
descent lamp,  268.  Edison  and  the  electric  light,  268. 

INDIVIDUAL  PROJECTS 269 

PROJECT  XIII.  HEATING  OUR  HOMES 

INTRODUCTION 271 

The  necessity  of  heat. 
PROBLEMS: 271 

TOPICS: 

Fuel,  275.  Wood  as  a  fuel,  275.  The  story  of  coal,  275.  How  to 
build  a  fire,  276.  The  best  temperature  for  houses,  276.  The  fireplace 


CONTENTS  xiii 

as  a  heater,  277.  Three  ways  of  distributing  heat,  277.  Radiation,  277. 
Conduction,  278.  Convection,  278.  A  stove  as  a  heater,  279.  A  hot- 
air  furnace,  280.  Hot-water  heating,  281.  Steam  heat,  282.  Gas 
heaters,  283. 

INDIVIDUAL  PROJECTS 284 

PROJECT  XIV.  CLOTHING  AND  ITS  CARE 

INTRODUCTION 286 

Where  our  clothes  come  from. 
The  science  of  clothing. 

PROBLEMS 287 

TOPICS: 

The  purpose  of  clothing,  293.  An  envelope  of  air  around  our  bodies, 
294.  Clothes  as  conductors  of  heat,  294.  Perspiration,  294.  The  cool- 
ing effect  of  evaporation,  295.  The  relation  between  color  of  clothing 
and  their  warmth,  296.  Waterproof  clothes,  296.  Makers  of  fibers, 

296.  Cotton,  the  leading  plant  fiber,  296.     Flax,  a  plant-stalk  fiber, 

297.  Other  plant  fibers,  297.     Wool,  298.     Silk,  298.     Artificial  silk, 
300.    Other  animal  resources  for  clothing,  300.     The  care  of  our  cloth- 
ing, 300.    Water  as  a  cleanser,  301.    The  action  of  soap,  301.     How 
to  remove  stains,  302.     Clothes  moths,  305. 

INDIVIDUAL  PROJECTS 305 

UNIT  V.    THE  WORK  OF  THE  WORLD 
PROJECT  XV.  WORK  WITH  EVERYDAY  MACHINES 

INTRODUCTION 307 

Machines  in  our  homes. 

PROBLEMS .      *.     .  308 

TOPICS: 

Necessary  work,  317.  Work  requires  energy,  318.  Work  requires 
force,  318.  Work  results  in  motion,  319.  Resistance  to  work,  319. 
Weight,  319.  Friction,  320.  Inertia,  321.  How  work  is  measured, 
321.  Simple  machines,  322.  The  lever,  322.  The  mechanical  advantages 
of  levers,  325.  The  efficiency  of  a  machine,  326.  A  modified  lever,  the 
crank  and  axle,  326.  Another  modified  lever,  the  pulley,  327.  The  in- 
clined plane,  328.  A  modified  inclined  plane,  the  wedge,  329.  The 
screw  —  an  inclined  plane,  329.  A  great  inventor,  Galileo,  330.  The 
invention  of  the  pendulum  clock,  330.  Complex  machines,  331. 

INDIVIDUAL  PROJECTS 331 


xiv  CONTENTS 

PROJECT  XVI.  COMMUNICATION 
INTRODUCTION         333 

Importance  of  communication  to  our  civilization. 
PROBLEMS 333 

TOPICS: 

Organs  of  speech,  337.  Writing  and  printing,  338.  Signaling,  339. 
Electricity  and  modern  methods  of  communication,  339.  Magnets  and 
lines  of  force,  340.  Like  poles  repel;  unlike  poles  attract,  340.  Per- 
manent and  temporary  magnets,  341.  The  compass  and  its  uses,  341. 
Lines  of  force  about  an  electric  wire,  342.  Making  an  electromagnet, 
342.  The  electric  bell,  343.  The  telegraph,  343.  Submarine  cables, 
344.  The  telephone,  345.  The  wireless  telegraph  and  telephone,  346. 
The  making  of  a  newspaper,  347. 

INDIVIDUAL  PROJECTS 348 

PROJECT  XVII.  TRANSPORTATION 

INTRODUCTION        . 349 

Importance  of  transportation  in  everyday  life. 

PROBLEMS 350 

TOPICS: 

Animal  power  compared  with  steam  and  electric  power,  352.  Water 
as  a  means  of  transportation,  352.  Why  substances  float  or  sink,  353. 
Archimedes'  principle,  354.  Specific  gravity,  355.  The  floating  of  iron 
ships,  355.  Submarines,  355.  Steam  engines,  356.  The  first  steam 
engine,  356.  How  a  steam  engine  works,  357.  The  locomotive  and 
the  steamship,  358.  Great  water  routes,  360.  Great  land  routes,  361. 
Steam  and  gas  engines  compared,  361.  How  a  gas  engine  works,  361. 
The  automobile,  362.  Electric  power,  365.  The  parts  and  working 
of  an  electric  motor,  366.  Electric  cars  and  locomotives,  366.  The 
dynamo  compared  with  an  electric  motor,  367.  The  principle  of  the 
dynamo,  368.  Power  stations,  368.  Kinds  of  water-wheels,  369.  For- 
ests regulate  the  flow  of  water,  370.  Methods  of  protecting  forests,  370. 

INDIVIDUAL  PROJECTS 371 

PROJECT  XVIII.  LIFE  — ITS  ORIGIN  AND  BETTERMENT 

INTRODUCTION 373 

The  changing  life  upon  the  earth. 

PROBLEMS 374 

TOPICS: 

All  life  comes  from  life,  376.  Methods  of  reproduction,  377.  Seeds  and 
eggs,  377-  A  baby  plant  in  the  making,  378.  The  parts  of  a  flower  and 


CONTENTS  xv 

their  work,  378.  How  a  part  of  the  pollen  grain  reaches  the  egg-cell,  379. 
Development  of  the  fertilized  egg,  380.  Summary  of  steps  in  the  de- 
velopment of  a  seed,  380.  Reproduction  in  higher  forms  of  animals,  381. 
Kinds  of  pollination,  381.  How  cross-pollination  is  accomplished,  383. 
Artificial  cross-pollination,  383.  The  meaning  of  heredity,  383.  The 
meaning  of  variation,  384.  Charles  Darwin  and  evolution,  384.  The 
meaning  of  selection,  384.  Improving  living  conditions,  386.  Preven- 
tive medicine,  386.  Vaccination  against  smallpox,  387.  Inoculation 
against  typhoid  fever,  387.  Destroying  flies,  387.  Destroying  mos- 
quitoes, 388.  Improving  your  own  environment,  390. 

INDIVIDUAL  PROJECTS 390 

SUGGESTIONS  TO  TEACHERS        .  393 

INDEX «» 412 


ACKNOWLEDGMENTS 

WE  wish  to  express  our  sincere  appreciation  to  all  who  have 
helped  in  the  making  of  this  book;  to  Oscar  C.  Gallagher,  Head 
Master  of  the  West  Roxbury  High  School,  Boston,  and  George 
W.  Hunter,  Head  of  Department,  DeWitt  Clinton  High  School, 
New  York,  who  encouraged  us  to  undertake  the  work;  to  Dr. 
Thomas  H.  Briggs,  of  Columbia  University,  who  as  editor  has 
carefully  read  the  proof  and  offered  valuable  suggestions;  to 
Leonard  O.  Packard,  Clarence  H.  Jones,  Bertha  B.  Bryant,  and 
Charles  Crane,  who  have  read  and  criticized  portions  of  the 
manuscript;  to  all  those  who  have  helped  in  the  reading  of 
the  proof;  to  Edna  Van  Buskirk,  who  has  rendered  invaluable 
assistance  throughout ;  and  to  Hanson  Hart  Webster,  who  by  his 
energy  and  constant  help  has  made  possible  its  publishing. 

For  the  illustrations  we  are  indebted  to  Frank  W.  Wheat  for  a 
large  number  of  line  drawings,  and  to  many  friendly  individuals 
and  companies  for  the  use  of  photographs  and  other  material. 
We  have  endeavored  to  give  correct  recognition  in  each  case ;  if 
errors  or  omissions  have  been  made  we  shall  appreciate  informa- 
tion which  will  enable  us  to  make  corrections  in  the  next  edition. 

THE  AUTHORS 


THE  SCIENCE  OF  EVERYDAY  LIFE 

PART  I.  THE  CHIEF  NECESSITIES  OF  LIFE 

INTRODUCTION 

Science  of  everyday  life.  The  world  about  us  is  full  of  inter- 
esting things.  Yet  to  some  people  it  may  seem  narrow  and  unin- 
teresting. Perhaps  the  most  common  reason  is  that  they  neither 
observe  nor  try  to  understand  the  meaning  of  really  wonderful 
everyday  happenings.  Thousands  of  boys  and  girls  ride  in  trolley 
cars  and  automobiles  every  day.  Thousands  daily  use  electric 
lights.  Yet  many  have  never  taken  the  time  to  find  out  just  why 
the  trolley  car  moves  or  the  electric  light  bulb  gives  light.  Almost 
every  one  uses  the  telephone,  but  how  many  know  how  it  works? 
A  wide-awake  boy  or  girl  ought  to  be  interested  in  learning  about 
such  things.  What  are  they  made  of?  How  do  they  work? 
Who  first  thought  of  and  invented  them?  Your  work  in  general 
science  should  show  you  how  to  acquire  this  kind  of  knowledge. 

Life's  chief  necessities.  By  careful  experiments  and  observa- 
tion it  has  been  found  that  every  plant  or  animal  needs  certain 
things  in  order  to  live.  They  are  not  exactly  the  same  for  all 
kinds  of  living  beings.  We  know  that  plants  need  some  things 
that  animals  do  not  need  and  that  animals  must  have  other 
things  that  plants  cannot  use.  Nevertheless,  there  are  three  es- 
sentials for  all.  They  are  air,  water,  and  food. 

If  you  consider  your  own  needs,  you  will  realize  how  true  this 
is.  If  our  supply  of  air  is  cut  off  for  only  a  few  minutes,  we  die  of 
suffocation.  Without  food  we  slowly  starve  to  death  and  with- 
out water  we  perish  of  thirst.  What  is  true  of  the  human  being 
is  also  true  of  plant  life.  A  tree,  for  example,  must  breathe.  It 
does  this  through  tiny  holes  in  its  leaves  and  twigs.  It  needs 
water  which  it  gathers  in  by  means  of  delicate  hairy  growths  on 


.INTRODUCTION  * 


its  roots.  Part  of,  its  .food  comes  from  the  soil  and  is  made  in 
the  leaves"^;  tli  eyi:r.e.e  itself.  >  Deprive  the  tree  of  any  of  these 
things  and  it  will  wither  and  die.  Because  of  the  fact  that  air, 

water,  and  food  are  what 
may  be  called  the  prime 
essentials  of  life,  they  have 
been  chosen  as  the  first 
topics  of  study. 

GROUP  OR  INDIVIDUAL  PRO- 
JECT: MAKE  A  BALANCED 
AQUARIUM  FOR  THE  SCHOOL- 
ROOM. 

An  aquarium  is ' '  balanced ' ' 
when  the  plants  and  animals 
are  in  just  the  right  propor- 
tion to  keep  the  water  sweet 
and  clean.  Such  an  aquarium 
requires  no  changing  of  the 
water. 

Be  sure  that  the  glass  is 
clean.  Put  in  about  two 
inches  of  clean  sand  or  peb- 
bles. Next  put  in  one  or  two 
water  plants  with  roots.  Ar- 
range pebbles,  shells,  or  stones  to  hold  the  roots  in  place.  Now  pour  in 
the  water,  slowly,  almost  to  the  top.  Let  it  stand  a  few  days. 

The  animals  may  now  be  added.  One  goldfish  and  a  couple  of  minnows 
are  enough  for  a  battery- jar  aquarium.  Be  sure  to  have  several  snails  or 
tadpoles  to  keep  the  water  clean.  Flatworms,  caddis-fly  larvae,  and  other 
insects  are  good  additions,  interesting  to  watch. 


FIG.  i.  A  school  aquarium.  The  living  creatures 
in  the  aquarium  need  air,  water,  and  food.  The  fish 
get  the  essential  gas  of  the  air  from  the  plants,  and 
food  from  invisible  organisms  in  the  water.  The 
plants  make  their  own  food. 

(Courtesy,  New  York  Zoological  Society.) 


UNIT  I 
THE  AIR  AND  HOW  WE  USE  IT 

PROJECT  I 
THE  AIR  A  REAL  SUBSTANCE 

Air  is  real.  Air  does  freakish  things  when  in  very  rapid  mo- 
tion. The  rushing,  whirling  air  of  a  tornado  sometimes  plucks 
the  feathers  from  chickens  and  drives  straws  into  wood.  Such 
windstorms  have  demolished  houses  and  twisted  trees  like  so 
much  twine.  We  have  all  seen  hats  blown  off  on  windy  days, 
and  we  have  all  stood  in  front  of  electric  fans  and  felt  the  air  be- 
ing moved  by  them.  Windmills,  sailing  vessels,  and  balloons  all 
depend  upon  moving  air.  The  airplane's  motion  depends  upon 
the  motion  of  the  propeller,  but  the  propeller  would  be  of  no  use 
if  it  had  no  resistance  to  wrork  upon,  and  it  is  the  air  which  fur- 
nishes this  resistance.  Such  facts  as  these  indicate  that  air,  even 
though  we  do  not  see  it,  is  real. 

Some  problems  to  solve.  A  question  asked  of  nature  and  an- 
swered by  nature  is  sometimes  called  an  "  experiment."  In  this 
book  we  call  it  a  "  problem."  The  mere  statement  that  air  is  real 
is  less  convincing  than  actual  proof  which  you  can  see  yourself. 
Try  the  first  three  problems  which  follow  if  you  would  be  sure  of 
its  reality.  To  find  some  ways  in  which  air  works  for  us,  try 
problems  6-10.  The  relation  between  air  pressure  and  the 
weather  and  the  dependence  of  sound  upon  air  you  may  find  by 
performing  the  experiments  suggested  in  problems  4, 5, 11,  and  12. 

As  you  attempt  to  solve  each  problem,  make  sure  that  you 
thoroughly  understand  what  you  wish  to  find  out,  so  that  you 
have  a  definite  end  or  goal.  Follow  the  directions  carefully;  ob- 
serve what  happens;  ask  yourself  the  meaning  of  what  you  ob- 
serve; and  so  reach  your  goal,  the  solution  of  the  problem. 


THE  AIR  AND  HOW  WE  "USE  IT 


Individual  projects.  Besides  solving  the  problems  and  study- 
ing the  projects  as  given  in  this  book,  some  of  you  will  be  glad  to 
do  more.  The  individual  projects  on  page  20  will  give  you  some 
suggestions.  You  may  wish  to  attempt  a  working  project,  such 
as  making  a  toy  airplane;  or  you  may  prefer  to  read  about  such 
subjects  as  man's  conquest  of  the  air,  and  report  to  the  class. 
Consult  your  teacher  as  to  your  choice;  then  do  your  best. 

PROBLEMS 

PROBLEM  i:  WHAT  is  IN  AN  "EMPTY"  GLASS? 

Directions: 

Procure  an  empty  glass  and  a  basin  of  water. 

Invert  the  glass  and  press  it  into  the  water  in  such  a  manner  as  not  to 
allow  any  bubbles  to  escape. 

Questions: 

1.  To  what  extent  does  the  water  rise  in  the  glass? 

2.  Why  does  it  not  fill  the  entire  glass? 

3.  What  does  this  experiment  show  about  air?     Explain. 

4.  If  you  permit  bubbles  to  escape,  does  the  water  then  rise  in  the  glass? 
Why? 

PROBLEM  2:  DOES  THE  AIR  WEIGH  ANYTHING? 

Directions: 

Blow  up  a  football  until  it  is  as  firm  as  possible.  What  is  in  the  football? 
Remove  one  pan  from  a  balance  and  hang  the  football  in  its  place.  Bal- 
ance it  with  sand  in  the  other  pan. 
Let  the  air  escape  from  the  foot- 
ball. Explain  what  happens  to 
the  pan  containing  sand. 

Conclusion: 
Does  the  air  weigh  anything? 

Question: 

Which  is  heavier,  an  automobile 
tire  pumped  hard,  or  a  punctured 
FIG.  2.  Does  air  have  weight?  tire? 

PROBLEM  3:  DOES  THE  AIR  EXERT  A  PRESSURE? 
Directions: 

Tie  a  piece  of  thin  rubber  tissue  tightly  over  the  top  of  a  glass  funnel 
tube.  Suck  in  from  the  stem  of  the  tube.  What  happens?  Why?  Hold 


THE  AIR  A  REAL  SUBSTANCE 

the  funnel  in  several  different  positions  and  repeat  the  experiment, 
what  direction  does  the  air  press? 

Dip  one  end  of  a  glass  tube  into  water  in  a  glass. 
Suck  some  of  the  air  from  the  tube.  What  happens? 
Why? 

Fill  a  glass  with  water.  Place  a  piece  of  cardboard 
over  the  top,  and  hold  it  there  while  you  invert  the 
glass.  Remove  your  hand  carefully.  Does  the  water 
flow  out  of  the  glass?  Why? 

Conclusion: 

Does  the  air  exert  a  pressure? 

Questions: 

1.  In  what  directions  is  the  pressure  exerted? 

2.  Why  will  a  swinging  door  move  slightly  if  you 
open  a  door  quickly  in  another  part  of  the  room? 


In 


PROBLEM  4:  How  CAN  AIR  PRESSURE  BE  MEASURED? 

Directions: 

Take  a  glass  tube  about  three  feet  long,  open  at 
one  end  and  closed  at  the  other.  Fill  the  tube  with 
mercury.  Hold  the  thumb  over  the  open  end  and 
invert  the  tube  in  a  cup  containing  mercury.  Re- 
move the  thumb  only  after  the  lower  end  of  the  tube 
is  below  the  level  of  mercury  in  the  cup. 

What  happens?  Measure  the  height  of  the  column 
above  the  level  of  mercury  in  the  cup. 

Questions: 

1.  Why  does  the  mercury  not  fall  all  the  way  in 
the  tube? 

2.  Why  does  it  fall  a  few  inches? 

3.  How  can  a  device  like  this  be  used  to  measure 
air  pressure? 

4.  Mercury  is  about  13.6  times  as  heavy  as  water. 
What  would  be  the  approximate  length  of  a  tube  for 
a  water  barometer? 


FIG.  3.  A  simple 
barometer. 


PROBLEM  5:  WHAT  is  THE  RELATION  BETWEEN  AIR  PRESSURE  AND  THE 
WEATHER? 

Diret^ions: 

Use  a  graph  paper  or  rule  off  squares  upon  a  blank  paper  according  to 
the  plan  shown  in  the  diagram  on  page  103. 


THE  AIR  AND  HOW  WE  TJSE  IT 


Decide  upon  a  certain  time  of  day  to  take  the  reading  of  the  barometer 
or  copy  the  official  report  as  given  in  the  newspaper. 

To  indicate  the  kind  of  weather  the  following  symbols  are  suggested: 
O  equals  Fair;  (i  equals  Partly  Cloudy;  ©  equals  Cloudy;  ©  equals 
Rain;  (D  equals  Snow. 

On  each  day  record  the  date,  the  kind  of  weather,  and  the  reading  of  the 
barometer. 

Questions: 

1.  Can  you  observe  any  relation  between  the  kind  of  weather  and  the 
rising  and  falling  of  the  barometer? 

2.  In  general,  what  is  indicated  by  a  rising  barometer?    By  a  falling 
barometer? 

PROBLEM  6:  WHY  DOES  WATER 
RISE  IN  A  PUMP? 

Directions: 

Part  i.  Use  a  fountain-pen  filler 
to  suck  up  some  liquid. 

What  makes  the  liquid  rise  af- 
ter the  pressure  upon  the  bulb  has 
been  released? 

Part  2.  From  a  model  or  from 
the  diagram  study  the  operation 
of  the  piston  and  the  valves  of  a 
suction  pump. 

Make  diagrams,  showing  the 
opening  and  closing  of  these  valves 
when  the  piston  is  in  different  po- 
sitions. 

Conclusion: 

Why  does  the  water  rise  in  the 
pump? 
Questions: 

1.  To  what  height  will  a  suction 
pump  lift  water? 

2.  Why  will  it  not  suck  it  any 
higher? 


FIG.  4.  A  pump.  A 
ing  down.  In  B  and  C, 
position  and  show  the 


shows  the  piston  mov- 
place  valves  in  proper 
level  of  .the  water. 


PROBLEM  7 :  How  DOES  A  FORCE  PUMP  WORK? 

Directions: 

From  a  model  or  from  the  diagram  on  page  7,  notice  the  following 
points : 

i.  The  arrangement  of  the  valves. 


THE  AIR  A  REAL  SUBSTANCE 


FIG.  5.  A  force  pump. 


2.  The  position  of  the  air  chamber,  if  one  is  present. 

3.  The  opening  and  closing  of  the  valves  and  the  course  taken  by  the  water. 

Questions: 

1.  For  what  purpose  are  force  pumps 
needed? 

2.  Of  what  use  is  the  air  chamber? 

Summary: 

Make  drawings  to  indicate  the  operation 
of  a  force  pump,  when  the  plunger  is  mov- 
ing up;  when  the  plunger  is  moving  down. 

PROBLEM  8:  To  USE  AN  EXHAUST  PUMP 

AND  SEE  HOW  IT  WORKS. 

Directions: 

Place  a  palm  glass  over  the  stand  of  an 
exhaust  or  air  pump.  Tie  a  piece  of  rubber 
sheeting  tightly  over  the  top  of  the  glass. 
Remove  some  of  the  air  from  the  glass. 

What  happens  to  the  rubber  sheeting?     Explain. 

Summary: 

Explain,  as  you  would  to  some  one  who  has  not  studied  it,  the  operation 
of  an  exhaust  pump. 

PROBLEM  9:  How  DOES  A  BICYCLE  PUMP  WORK? 

Directions: 

Place  a  finger  over  the  end  of  the  tube  leading  from  the  pump  and  no- 
tice at  what  times  the  air  is  expelled  and  also  when  a  suction  is  produced. 

Take  the  pump  apart  and  examine  the  manner  in  which  the  plunger 
operates  in  the  cylinder. 

Notice  the  arrangement  for  taking  in  more  air  to  be  forced  into  the 
tube.  What  special  arrangement  in  the  tire  prevents  the  air  from  being 
sucked  back  into  the  cylinder  from  the  tire  when  the  pump  is  attached 
and  operating? 

Summary: 

Make  labeled  drawings  of  a  bicycle  pump  in  different  positions  to  indi- 
cate its  manner  of  operation. 

PROBLEM  10:  To  TAKE  WATER  OUT  OF  AN  AQUARIUM  BY  USING  A  SIPHON. 

(If  there  is  no  aquarium,  use  a  jar.) 
Directions: 

Fill  a  piece  of  rubber  tubing  of  convenient  length  with  water,  holding 
the  thumb  over  the  ends. 


8  THE  AIR  AND  HOW  WE*  USE  IT 

Still  holding  the  thumb  over  the  openings,  place  one  below  the  surface 
of  the  water  in  the  aquarium.  Put  the  other  opening  into  a  receptacle 
which  is  below  the  level  of  the  aquarium.  What  happens? 

Gradually  raise  the  end  of  the  tube  from  which  water  is  flowing  and 
note  result. 

Questions: 

1.  Can  you  explain  why  the  water  should  flow  up  and  out  of  the  aqua- 
rium? 

2.  Under  what  conditions  will  the  water  stop  flowing?     Why? 

3.  How  could  you  remove  water  from  a  boat  on  the  beach  without 
tipping  it  over  or  bailing  it  out? 

PROBLEM  n:  To  STUDY  A  MODEL  OR  DIAGRAM  OF  THE  HUMAN  EAR. 

Directions: 

From  a  study  of  a  model  or  from  the  diagram  on  page  15,  answer  the 
following  questions: 

Locate  the  outer,  middle,  and  inner  ears. 

What  separates  the  outer  from  the  middle  ear?  Of  what  use  is  this 
structure? 

Has  the  middle  ear  any  connection  with  the  exterior?     If  so,  what? 

Questions: 

1.  What  is  the  usual  outside  pressure  upon  the  ear  drum?    What  is  the 
usual  inside  pressure  upon  the  ear  drum?    Explain. 

2.  When  an  aviator  rises  rapidly  above  the  earth's  surface  upon  which 
side  of  the  ear  drum  will  there  first  be  a  change  in  pressure?    Why?   Will 
there  be  a  lower  or  increased  pressure  from  the  exterior?    Explain  what 
happens  to  the  ear  drum  when  he  descends  rapidly. 

3.  Why  do  colds  sometimes  cause  a  slight  deafness? 

PROBLEM  12:  Is  AIR  NECESSARY  FOR  THE  TRANSMISSION  OF  SOUND? 

Directions: 

By  means  of  an  exhaust  pump  remove  as  much  of  the  air  as  possible 
from  a  bell  jar  in  which  an  electric  bell  has  been  set  ringing. 

As  the  amount  of  air  in  the  bell  jar  is  decreased  what  is  the  effect  upon 
the  amount  of  sound  produced  by  the  clapper  hitting  the  bell? 

Conclusion: 
What  is  your  conclusion  regarding  the  ability  of  air  to  transmit  sound? 

Three  forms  of  matter.  The  world  in  which  we  live  is  made  up 
of  three  forms  of  matter:  solids,  liquids,  and  gases.  A  piece  of 
rock  and  a  glass  of  water,  which  we  may  consider  as  illustrations 


THE  AIR  A  REAL  SUBSTANCE 


of  solids  and  liquids,  can  be  seen  and  handled.  We  know  that  they 
occupy  space  and  are  real,  but  a  jar  full  of  air,  which  is  composed 
of  invisible  gases,  we  ordinarily  refer  to  as  empty.  Is  this  cor- 
rect? When  an  inverted  "  empty  "  jar  is  evenly  pressed  down 
into  a  basin  of  water,  practically  no  water  will  enter  the  jar.  If 
we  wish  to  have  water  enter 
the  jar,  the  air  must  first  be 
allowed  to  escape  by  coming 
to  the  surface  of  the  water  in 
the  form  of  bubbles.  Does 
not  the  result  of  this  simple 
experiment  indicate  that  air 
is  real? 

The  atmosphere  an  ocean 
of  air.  We  are  all  living  at 
the  bottom  of  an  ocean  of  air. 
This  ocean  of  air,  extending 
approximately  two  hundred 
miles  above  our  heads,  is  com- 
posed of  just  as  real  a  sub- 
stance as  any  ocean  of  water. 
Furthermore,  just  as  water 
exerts  more  and  more  pressure 
as  its  depth  increases,  because 
it  has  weight,  for  the  same 
reason  the  ocean  of  air  exerts 
pressure  which  increases  with 
its  depth.  Thus  the  air  does 
not  exert  as  great  pressure  on 
the  top  of  a  mountain  as  in  a 
valley.  This  is  because  there 
is  more  air  pressing  down 
upon  any  place  in  the  valley 
than  upon  any  place  of  simi- 
lar size  upon  the  mountain.  As  the  air  completely  surrounds  the 
earth  and  fills  every  crack  and  crevice,  there  is  pressure  exerted 
upon  all  parts  of  the  earth's  surface.  It  has  been  found  that  this 


FIG.  6.  The  ocean  of  air. 


io  THE  AIR  AND  HOW  WE  -USE  IT 

air  weight  or  pressure  at  sea-level  is  about  fifteen  pounds  to  every 
square  inch. 

Air  pressure.  Galileo,  a  great  Italian  scientist  of  the  sixteenth 
century,  was  one  of  the  first  men  to  have  a  correct  idea  about  air 
pressure.  He  had  a  suction  pump  which  would  not  work  when 
the  water  was  low  in  the  well.  He  sent  for  a  mechanic  to  have  it 
fixed,  but  was  told  that  the  pump  was  in  good  condition  and 
that  no  suction  pump  could  be  operated  when  the  water  must  be 
raised  much  over  twenty-five  feet.  The  mechanic  could  not  ex- 
plain why  this  was  so,  but  Galileo  believed  that  it  was  because 
the  air  pressure  was  not  great  enough  to  raise  it  any  higher.  He 
then  set  one  of  his  pupils,  Torricelli,  to  work  upon  this  problem. 

Torricelli  proved  that  Galileo's  idea  about  air  pressure  was 
correct,  that  it  will  support  a  column  of  water  about  thirty-four 
feet  high.  If  a  perfect  suction  could  be  produced,  a  pump  thirty- 
four  feet  in  length  might  be  operated.  He  also  found  that  the  air 
pressure  at  sea-level  was  sufficient  to  hold  up  a  column  of  mer- 
cury about  thirty  inches  in  height.  As  a  result  of  this  experiment 
we  have  the  instrument  called  the  barometer. 

Making  a  mercurial  barometer.  A  barometer  is  an  instrument 
for  measuring  the  weight  or  pressure  of  the  air.  Torricelli  took 
a  glass  tube  about  three  feet  long,  open  at  one  end  and  closed  at 
the  other.  He  filled  it  with  mercury,  which  is  a  very  heavy  liquid, 
13.6  times  as  heavy  as  water.  Then,  holding  his  thumb  over  the 
open  end,  he  inverted  it  in  a  cup  of  mercury,  removing  his  thumb 
only  after  the  lower  end  of  the  tube  was  below  the  level  of  mercury 
in  the  cup.  The  column  of  mercury  dropped  in  the  tube  until 
the  top  of  it  was  about  thirty  inches  above  the  level  of  mercury 
in  the  cup.  This  column  of  mercury  balances  a  column  of  air  as 
high  as  the  atmosphere  extends. 

The  barometer  used  to  indicate  height.  Blaise  Pascal,  a 
Frenchman  who  lived  about  the  same  time  as  Torricelli,  dis- 
covered how  to  tell  the  elevation  of  a  place  by  means  of  the 
barometer.  He  and  a  company  of  friends  ascended  a  mountain, 
leaving  a  barometer  at  the  bottom  and  taking  another  with  them. 
They  found  that  when  they  reached  the  summit  of  the  mountain 
the  level  of  the  top  of  the  column  of  mercury  had  fallen  about 


THE  AIR  A  REAL  SUBSTANCE 


ii 


three  inches.  They  knew  they  had  gone  up  twenty-seven  hun- 
dred feet.  Then  they  carried  the  barometer  down  the  mountain 
and  found  that  when  they  had  gone  halfway  down,  the  mercury 
had  moved  up  the  tube  to 
a  place  an  inch  and  a  half 
higher  than  it  was  when 
they  had  started  to  de- 
scend. When  they  reached 
the  bottom  they  found 
that  the  two  barometers 
registered  the  same  — 
about  thirty  inches  above 
the  level  of  mercury  in  the 
cups.  Thus  it  was  dis- 
covered that  for  a  rise  of 
every  nine  hundred  feet 
near  the  earth's  surface 
there  is  a  decrease  of  pres- 
sure represented  by  a  one- 
inch  drop  of  the  mercury 
in  the  tube. 

The  aneroid  barome- 
ter. At  the  present  time 
another  kind  of  barome- 
ter is  manufactured  which 
is  more  easily  carried. 
This  newer  kind  of  ba- 
rometer contains  no  li- 
quid and  hence  is  called 
aneroid  —  a  word  which 
comes  from  two  Greek 
words,  meaning  without 
moisture.  Its  action  de- 
pends upon  the  motion  of 


FIG.  7.  An  aneroid  barometer.  The  upper  view 
shows  the  appearance.  The  diagram  below  shows 
the  parts.  A  change  of  pressure  on  the  vacuum  box 
causes  the  mainspring  to  move  and  the  pointer  to 
swing  around  the  dial. 

(Courtesy  Taylor  Instrument  Companies,  and 
U.S.  Bureau  of  Standards.) 


a  pointer  which  is  regulated  by  air  pressure  upon  a  metal  disk. 
Aviators  and  balloonists  take  this  latter  type  of  barometer  with 
them  to  indicate  how  far  above  the  earth's  surface  they  have  risen. 


12  THE  AIR  AND  HOW  WE 'USE  IT 

The  barometer  used  to  forecast  weather.  The  air  pressure  at 
any  one  place  is  not  always  the  same,  but  fluctuates  or  changes 
constantly.  (See  page  1 1 1 .)  The  causes  of  these  fluctuations  are 
closely  connected  with  weather  conditions,  and  for  that  reason 
the  barometer  is  widely  used  to  forecast  the  weather.  The  sub- 
ject of  the  barometer  in  relation  to  the  weather  is  too  large  a  one 
for  us  to  take  up  further  here.  It  must  be  sufficient  here  to  state 
that  in  general  a  rising  barometer  indicates  clear  weather  while 
a  falling  barometer  indicates  approaching  storm. 

Air  pressure  and  the  suction  pump.  One  very  common  imple- 
ment the  operation  of  which  depends  upon  the  air  pressure  is  the 
ordinary  pump.  This  is  in  general  use  all  over  the  country  to 
draw  water  out  of  shallow  wells.  It  is  called  the  suction  pump 
because  its  proper  working  depends  upon  a  closely  fitting  piston 
in  a  tube  in  which  water  is  lifted  by  means  of  suction.  By  suc- 
tion is  meant  the  action  of  air  pressure  in  forcing  t^he  water  up  into 
a  space  from  which  the  air  has  previously  been  drawn  out.  If  you 
will  study  figure  4,  the  principle  underlying  its  construction  and 
operation  will  become  clear. 

The  force  pump.  As  the  name  implies,  the  force  pump  is  used  to  force 
the  water  up  to  a  higher  level  than  can  be  reached  by  the  ordinary  suction 
pump.  Figure  5  indicates  the  position  of  the  valves  and  the  manner  in 
which  they  work.  Steam  fire  engines  have  force  pumps.  Why?  Force 
pumps  are  often  used  in  houses  which  are  not  supplied  with  water  pipes 
from  a  reservoir,  but  which  must  get  water  from  wells  by  the  use  of  suction 
pumps.  Using  a  force  pump  in  such  a  house  makes  it  possible  to  have 
running  water,  because  water  can  then  be  forced  into  a  tank  from  which 
it  may  be  made  to  flow  through  pipes  to  other  parts. 

The  use  of  an  air  chamber  in  a  force  pump  makes  the  water  flow  steadily 
instead  of  jerkily.  The  air  acts  as  a  cushion  and  tends  to  squeeze  the 
water  along  because  of  the  fact  that  it,  itself,  will  not  readily  contract 
and  when  contracted  tends  immediately  to  expand  and  occupy  more  space. 
In  other  words,  the  air  is  elastic. 

Air  pressure  and  the  exhaust  pump.  The  exhaust  pump  is  so  made  as 
to  be  able  to  remove  air  from  anything  to  which  it  may  be  attached.  Otto 
von  Guericke,  who  lived  at  about  the  time  of  Galileo,  invented  the  exhaust 
pump  and  performed  many  experiments  that  amazed  the  people  of  his  day. 
One  of  the  most  famous  of  these  was  performed  with  the  halves  of  a  hollow 
metal  sphere.  These  were  made  so  that  when  fitted  together  they  became 
air-tight.  Upon  attaching  his  exhaust  pump  to  them  he  was  able  to  re- 


THE  AIR  A  REAL  SUBSTANCE  13 

move  practically  all  the  air  from  inside.  When  this  was  done  it  was  not 
only  impossible  for  a  man  to  separate  those  halves,  but  it  is  reported  that 
thirty  horses,  although  hitched  together  so  as  to  exert  their  combined 
strength  to  pull  the  hemispheres  apart,  were  unable  to  do  so.  Yet  when 
air  was  permitted  to  enter  they  fell  apart  of  their  own  weight.  How  do 
you  explain  these  facts? 

The  bicycle  pump.  Bicycle  pumps  are  so  commonly  used  that 
we  ought  to  be  familiar  with  their  mechanism.  The  one  shown 
in  the  diagram  is  the  simplest,  but  there  are  several 
modifications  of  this.  When  the  piston,  which  is 
made  of  rubber,  is  pushed  down,  the  rubber  is 
squeezed  tightly  against  the  sides  of  the  cylinder, 
while  on  the  up-stroke  the  rubber  piston  is  some- 
what loose.  Can  you  explain  the  use  of  this  in  the 
operation  of  the  pump? 

Air  pressure  and  the  action  of  the  siphon.  An- 
other instrument  which  depends  for  its  operation 
upon  the  action  of  air  pressure  is  the  siphon.  A 

siphon  is  a  bent  tube  that  is  used  for  conveying  a  _ 

FIG.  8.  A  bicycle 
liquid  upwards  and   then  downwards  to  a  lower          pump. 

level  than  that  originally  held  by  the  liquid.  The 
operation  of  the  siphon  depends  upon  a  difference  in  pressure 
at  the  ends  of  the  tube.  Since  the  air  pressure  is  approximately 
the  same  at  both  ends  of  the  tube,  the  difference  in  the  pressures 
at  these  points  must  be  due  to  the  difference  in  the  water  pres- 
sures in  the  arms  of  the  tubes.  The  pressure  of  the  column  of 
water  in  the  out-going  arm  is  greater  than  in  the  in-coming  arm. 
This  results  in  producing  a  suction  with  the  result  that  the  water 
flows  out  of  the  vessel  as  long  as  the  receiving  vessel  is  on  a 
lower  level. 

Pressure  on  the  human  body.  When  you  consider  the  great 
weight  of  air  which  is  pressing  down  upon  all  objects  on  the  earth's 
surface,  do  you  not  wonder  why  the  human  body  is  not  crushed 
beneath  it?  This  would  undoubtedly  happen,  were  it  not  for  the 
fact  that  (i)  the  air  pressure  is  exerted  not  simply  downward  but 
equally  in  all  directions ;  and  (2)  that  there  is  an  internal  pressure 
which  is  usually  equal  to  the  external  pressure.  At  times,  how- 


THE  AIR  AND  HOW  WE  USE  IT 


ever,  the  internal  and  external  pressures  are  not  equal.  Under 
such  circumstances  harmful  results  may  follow. 

Perhaps  you  have  experienced  unpleasant  sensations  in  the 
ears  as  a  result  of  using  fast  elevators  in  tall  buildings.  Some- 
times men  have  gone  up  so  far 
and  so  rapidly  in  balloons  as  to 
cause  bleeding  at  the  nose  and 
even  rupture  or  breaking  of  the 
ear  drums.  If  the  change  oc- 
curs slowly  the  body  has  time 
to  adjust  itself;  that  is,  the  in- 
ternal pressure  can  be  made 
equal  to  'the  external  pressure. 
If  the  change  occurs  rapidly, 
such  an  adjustment  is  impos- 
sible. Thus,  the  bleeding  from 
the  nose  in  the  case  of  men  who 
make  very  rapid  ascension  in 
balloons  is  caused  by  the  pres- 
sure in  the  blood  being  greater 
than  the  pressure  outside.  This 
causes  the  blood  to  ooze  through 
the  delicate  lining  of  the  inte- 
rior of  the  nose.  Likewise  if  one 
goes  downward  very  far  and 
very  rapidly,  unpleasant  sensa- 
tions are  experienced. 

Structure  of  the  human  ear. 
In  order  to  understand  how 
ringing  in  the  ears  may  be 
caused  in  connection  with  ra- 
pid changes  of  air  pressure,  it 

is  necessary  first  to  learn  something  about  the  structure  of  the 
ear.  This  organ  consists  of  three  parts.  There  is  the  external 
ear,  consisting  of  the  part  we  can  see,  together  with  the  channel 
running  into  the  head,  most  of  which  is  also  visible  from  the 
outside.  This  channel  is  stopped  by  a  membrane  called  the  ear 


FIG.  9.  Working  in  a  caisson.  Men  are 
enabled  to  work  under  water  by  means  of 
sunken  chambers  furnished  with  compressed 
air.  A  pressure  equal  to  four  times  that  of 
the  atmosphere  can  be  borne  by  the  human 
body.  Serious  illness  may  result  if  a  man 
comes  quickly  to  the  surface. 


THE  AIR  A  REAL  SUBSTANCE  15 

drum.  The  vibration  or  rapid  moving  backwards  and  forwards 
of  the  ear  drum  is  the  first  step  in  the  process  of  hearing.  The 
second  part  of  the  ear,  called  the  middle  ear,  is  directly  behind 
the  ear  drum.  Here  there  are  three  very  small  bones  which  are 
connected  with  each  other  and  with  the  ear  drum  in  such  a  way 
that  when  the  ear  drum  vibrates  the  bones  are  set  vibrating  in 
harmony  with  it.  These  vibrations  in  turn  are  carried  to  the  inner 
or  internal  ear.  In  this  part  of  the  ear  there  are  nerves  which  are 
affected  by  these  vibrations  in  such  a  manner  as  to  send  messages 
to  the  brain.  Hearing  is  the  result  of  the  whole  process. ' 

A  structure  not  shown  in  the  diagram,  called  the  Eustachian 
tube,  runs  from  the  back  of  the  throat  cavity  to  the  middle  ear 
where  the  three  bones  re- 
ferred to  are  located.     The 
function,  or  work,  of  this 
tube   is   to  permit  outside 
air  to  reach  the  middle  ear. 

Since  one  side  of  the  ear 
drum  is  freely  exposed  to 
the  outside  air  and  the  other 
side  is  not  so  directly  ex- 
posed, when  there  is  a  rapid 

change  in  air  pressure,  the  FlG-  10-  Parts  of  the  human  ear.    The  three 

,  •  j     .,«  bones  in  the  middle  ear  are  named,  from  their 

membrane  is  pressed  either      shapes>  the  hammer,  anvil,  and  stirrup.  The 

in  or  OUt.      Under  such  Cir-       cochlea,  shaped  like  a  shell,  is  in  the  internal  ear. 

cumstances  insufficient  time 

is  given  for  the  air  of  a  different  pressure  to  make  its  way  through 
the  Eustachian  tube  so  that  the  pressures  on  both  sides  of  the 
ear  drum  may  be  equal.  The  bulging  of  the  ear  drums  causes 
the  unpleasant  sensations  called  ringing  in  the  ears.  The  differ- 
ence in  pressure  may  become  great  enough  actually  to  cause  the 
rupture  or  bursting,  of  the  membrane.  Men  who  fire  the  big 
guns  in  battle  open  their  mouths  wide  at  the  instant  of  firing. 
Can  you  see  why? 

Air  transmits  sound.  Another  evidence  that  air  is  a  real  sub- 
stance is  the  fact  that  sound  can  travel  through  it.  In  order  to 
prove  that  air  is  a  real  substance  because  sound  may  be  trans- 


16 


THE  AIR  AND  HOW  WE  USE  IT 


mitted  through  it,  we  must  first  show  that  sound  does  not  travel 
through  a  vacuum,  a  space  where  literally  there  is  nothing.  This 
may  be  done  by  creating  as  perfect  a  vacuum  as  possible  and  then 
trying  to  pass  sound  through  it.  By  using  an  exhaust  pump  air 
may  be  removed  from  a  bell  jar  in  which  an  electric  bell  has  been 
set  ringing.  The  sound  of  the  bell  grows  fainter  and  fainter  as 
the  air  is  pumped  out.  As  a  complete  vacuum  is  impossible  under 
these  circumstances,  the  sound  of  the  bell  may  not  entirely  cease. 
However,  the  result  of  the  experiment  is  sufficient  to  cause  us  to 
infer  that  sound  will  not  travel  through  a  vacuum. 

The  nature  of  sound.  Any  object  that  gives  forth  sound  must 
be  vibrating;  that  is,  moving  backwards  and  forwards  very  rapidly. 

Thus,  to  make  a  tuning-fork  emit  sound 
it  must  be  struck  and  held  in  such  a 
manner  that  it  may  vibrate.  Simi- 
larly, the  materials  of  which  musical 
instruments  are  made  must  be  set  vi- 
brating in  order  to  produce  what  is 
called  music.  The  sounds  made  by  the 
human  voice  are  also  produced  by  vi- 
brations of  what  are  known  as  vocal 
cords.  These  vocal  cords  are  located 
in  the  upper  part  of  the  wind-pipe,  a 
place  commonly  spoken  of  in  man  as 
the  Adam's  apple.  But  not  only  must 
there  be  vibrations  to  produce  sound, 
there  must  be  also,  as  we  have  seen,  a 
medium  for  carrying  these  vibrations 
away  from  the  object  which  is  making  them.  The  air  is  the  usual 
medium  for  doing  this.  The  vibrations  pass  through  the  air  in 
what  are  called  sound  waves,  much  the  same  as  ripples  spread 
out  from  the  place  where  a  stone  has  been  thrown  into  a  pond, 
only  much  more  rapidly. 

The  rate  at  which  sound  travels.  It  has  been  found  that  sound 
travels  through  the  air  at  the  rate  of  a  little  less  than  eleven  hun- 
dred feet  per  second.  It  is  often  possible  to  compute  distances 
by  knowing  the  rate  at  which  sound  travels.  For  example,  if  you 


FIG.  n.   A  tuning-fork  sending 
vibrations  into  the  air. 


THE  AIR  A  REAL  SUBSTANCE 


were  standing  on  the  shore  of  a  lake  and  wished  to  know  the  dis- 
tance from  you  of  a  steamboat  that  happened  to  be  whistling, 
you  could  observe  the  instant  the  steam  escaped  and  then  count 
the  number  of  seconds  before  hearing  the  whistle.  An  interval  of 
five  seconds  would  indicate  that  the  boat  was  about  a  mile  away. 
Again,  in  a  thunderstorm  it  is  interesting  to  compute  how  far  away 
the  storm  is.  Since  light  travels  almost  instantaneously,  this 
can  be  done  by  counting  the  number  of  seconds  elapsing  be- 
tween the  flash  of  lightning  and  the  clap  of  thunder.  If  you  can 
count  ten  seconds  between  the  flash  of  lightning  and  the  sound 
of  thunder,  how  far  away  is  the  lightning  discharge? 

Compressed  air.  For  many  years  use  has  been  made  of  an- 
other characteristic  of  the  air ;  namely,  that  it  may  be  compressed 
in  volume,  that  is,  made  to  occupy  a  smaller  space  than  usual. 
Reference  has  already  been  made  to  one  instance  of  this  kind.  Do 
you  remember  what  it  was?  When  air  is  compressed  the  amount 
of  force  which  it  exerts  may  be  tremendous.  Every  one  is  familiar 
with  the  fact  that  bicycle  tires  and  most  automobile  tires  are  so 
made  as  to  permit  of  air  being  pumped  into  them.  The  air 
then  exerts  the  pressure  which  keeps  the  tires  properly  distended. 
Perhaps  you  may  have  wondered  at  the  great  amount  of  air 
which  such  tires  are  able  to  hold  without  breaking.  Another 
common  way  in  which 
compressed  air  is  used  is 
to  operate  the  air-brakes 
of  trains.  Compressed  air 
has  even  been  used  to  run 
cars  carrying  people.  It  is 
frequently  used  to  drive 
drills  into  rock  for  the 
purpose  of  blasting,  thus 
facilitating  the  construc- 
tion of  tunnels,  such  as 
the  great  tunnels  through 
the  Alps.  The  many  uses 

to  which  'compressed  air  has  been  put  would  make  a  good  pro- 
ject for  a  special  report. 


FIG.  12.  A  kettle  of  liquid  air  boiling  on  a  block 
of  ice.    (Courtesy,  Professor  Louis  Derr.) 


18 


THE  AIR  AND  HOW  WE 'USE  IT 


Liquid  air.  Another  evidence  that  air  is  real  is  found  in  the  fact  that  it 
may  be  made  to  take  a  visible  form.  By  subjecting  air  to  a  very  low  tem- 
perature —  much  below  freezing  point  —  it  has  been  found  possible  in 
recent  years  to  turn  air  into  a  liquid.  When  it  is  in  the  form  of  a  liquid 
it  is  called  liquid  air.  Liquid  air  tends  to  go  back  into  a  gaseous  state  very 
readily  unless  the  surrounding  temperature  is  kept  very  low.  When  air 
is  made  to  pass  from  a  gaseous  form  into  a  liquid  and  then  back  again  into 
its  original  condition,  none  of  it  is  lost  in  the  process,  although  in  a  liquid 
state  it  occupies  much  less  space.  If  all  of  the  air  making  up  our  atmos- 
phere could  be  liquefied,  the 
earth  would  be  covered  wjth 
an  ocean  of  liquid  air,  the 
depth  of  which  would  be  about 
thirty-five  feet,  instead  of  be- 
ing covered  as  it  now  is  with 
a  gaseous  ocean  probably 
more  than  two  hundred  miles 
in  depth. 

Balloons.  For  centuries 
man  has  been  trying  to 
"  fly."  He  long  ago  dis- 
covered that  anything 
which  was  lighter  in  weight 
than  an  equal  volume  of 
air,  would  rise  in  the  air. 
Balloons  have  thus  been 
made  large  enough  for 
men  to  take  trips  in  them. 
Balloons  are  merely  bags 
filled  with  some  gas  lighter 
than  air,  usually  hydro- 
gen. Passenger  balloons 
are  made  with  bags  large 

enough  to  support  the  basket  or  "  car  "  with  its  human  occu- 
pant. A  balloon  will  rise  until  it  reaches  a  place  where  it  is  just 
as  heavy  as  an  equal  volume  of  air  around  it.  It  will  go  no 
higher  unless  it  is  made  lighter  by  throwing  out  ballast.  When 
the  balloonist  wishes  to  come  down,  he  lets  out  some  of  the  gas 
from  the  big  bag  which  buoys  him  up.  The  balloon  then 


FIG.  13.  An  American  observation  balloon. 


THE  AIR  A  REAL  SUBSTANCE 


becomes  relatively  heavier  than  the  surrounding  air  and  conse- 
quently sinks. 

Airplanes.  The  balloon,  however,  driven  about  at  the  mercy 
of  the  wind,  is  a  poor  substitute  for  the  way  in  which  a  bird  flies, 
and  it  has  been  the  flight  of  the  bird  which  man  tried  for  many 
years  to  imitate.  The  bird,  however,  is  heavier  than  an  equal 
volume  of  air.  In  trying  to  imitate  the  bird,  therefore,  man  had 
to  solve  the  problem  of  how  to  make  a  machine  heavier  than 
air  which  yet  would  stay  up  in  the  air.  The  invention  and  the 
perfecting  of  the  light  gasoline  engine  finally  made  it  possible  to 
build  such  a  machine.  In 
1905  the  first  successful 
flying  machine  was  in- 
vented by  Wilbur  and  Or- 
ville  Wright,  of  Dayton, 
Ohio. 

The  motion  of  the  air- 
plane depends  upon  the 
resistance  offered  by  the 
air  to  the  revolving  pro- 


FIG.  14.  A  modern  airplane. 


pellers.  The  machine  is 
pushed  forward  while  the 
air  is  pushed  backward,  just  as  a  boat  is  sent  through  the  water 
by  pushing  the  water  backwards  by  means  of  oars,  paddle-wheels 
or  propellers.  It  is  as  if  an  electric  fan  were  made  so  as  to  be 
able  to  move  forward  instead  of  remaining  stationary.  The  push 
of  the  air  upon  the  fan,  if  made  to  revolve  fast  enough,  would 
cause  it  to  move.  By  a  proper  arrangement  of  planes  and  steer- 
ing appliances,  it  might  be  made  to  travel  through  the  air.  The 
airplane  is  made  in  a  similar  way.  To  obtain  from  the  air  the 
resistance  which  is  necessary  for  its  successful  operation,  there 
must  be  a  proper  balance  of  the  planes.  The  important  thing 
to  remember  from  our  present  point  of  view  is  that  the  move- 
ment of  airplanes  proves  that  the  air  is  real. 


20  THE  AIR  AND  HOW  WE  USE  IT 

INDIVIDUAL  PROJECTS 

Working  projects: 

1.  Make  a  kite  and  fly  it.     For  directions  see 

The  Field  and  Forest  Handy  Book.  D.  C.  Beard.  Chas.  Scribner's 
Sons. 

Home-Made  Toys  for  Girls  and  Boys.  A.  N.  Hall.  Norwood  Press,  Nor- 
wood, Mass. 

The  Outdoor  Handy  Book.     D.  C.  Beard.     Chas.  Scribner's  Sons. 

Practical  Things  with  Simple  Tools.    M.  Goldsmith.    Sully  &  Kleinteich. 

2.  Make  a  toy  windmill.     Directions  are  given  in 

Practical  Things  with  Simple  Tools.    M.  Goldsmith.    Sully  &  Kleinteich. 

3.  Make  a  toy  airplane.     Directions  in 

Practical  Things  with  Simple  Tools.    M.  Goldsmith.    Sully  &  Kleinteich. 

4.  Demonstrate  how  a  vacuum  cleaner  works  and  explain  its  mechanism. 
Write  to  a  manufacturing  company  for  descriptive  catalogue. 

Reports: 

1.  Pneumatic  mail  tubes. 

Harper's  Machinery  Book  for  Boys.     J.  H.  Adams.     Harper  &  Bros. 

2.  Liquid  air. 

Boys'  Book  of  Inventions.     R.  S.  Baker.   Doubleday  &  McClure. 

The  Romance  of  Modern  Inventions.    A.  Williams.    J.  B.  Lippincott  Co. 

Wonders  of  Science.     E.  M.  Tappan,  Editor.     Houghton  Mifflin  Co. 

3.  Work  and  life  of  Galileo. 

The  Story  of  Great  Inventions.     E.  E.  Burns.     Harper  &  Bros. 

4.  Compressed  air  and  its  uses. 

Wonders  of  Modern  Mechanism.    C.  H.  Cochrane.   J.  B.  Lippincott  Co. 

5.  Man's  conquest  of  the  air. 

The  Air  Man.     F.  A.  Collins.     Century  Co. 
Boys1  Book  of  Airships.    H.  Delacombe.    Fred.  A.  Stokes  Co. 
Boys'  Book  of  Model  Airplanes.     F.  A.  Collins.     Century  Co. 
Careers  of  Danger  and  Daring.     C.  Moffett.     Century  Co. 
How  It  Flies.     Richard  Ferris.     Thos.  Nelson  &  Sons. 
Stories  of  Inventors.     Russell  Doubleday.     Doubleday,  Page  &  Co. 
The  Story  of  the  Airplane.    C.  Grahame-White.    Small,  Maynard  &  Co. 
Wonders  of  Modern  Mechanism.    C.  H.  Cochrane.   J.  B.  Lippincott  Co. 
"The  American  Conquest  of  the  Air."    Norton.    Scientific  American, 
March  4,  1916. 

6.  Working  in  caissons. 

How  It  Is  Done.     Archibald  Williams.     Thos.  Nelson  &  Sons. 

7.  A  visit  to  a  pumping  station.     Visit  a  pumping  station  if  there  is  one  in 
the  community.     Obtain  as  much  information  about  it  as  possible  and 
make  a  report  in  class. 

BOOKS  THAT  WILL  HELP  YOU 

The  Barometer  as  the  Footrule  of  the  Air.    Taylor  Instrument  Cos.,  Roches- 
ter, New  York. 

The  Barometer  Book.     Taylor  Instrument  Cos.,  Rochester,  New  York. 
The  Wonder  Book  of  the  Atmosphere.     E.  J.  Houston.     Fred.  A.  Stokes  Co. 


PROJECT  II 
AIR  AND  FIRE 

Fire  in  its  relation  to  our  lives.  We  cannot  imagine  living  with- 
out fire.  As  far  back  as  the  history  of  man  can  go,  there  have 
been  no  savage  tribes  so  ignorant  that  they  did  not  know  about 
fire.  Primitive  man  made  a  god  of  it,  and  several  ancient  reli- 
gions are  based  upon  "  fire-worship."  Civilization  began  with 
the  discovery  of  fire  and  has  grown  with  the  increase  of  its  uses. 
We  use  it  in  our  homes  to  keep  us  warm,  to  cook  our  food,  and  to 
give  us  light.  We  use  it  in  our  communities  to  run  our  steam  en- 
gines, and  electric  dynamos,  which  in  turn  furnish  the  power 
for  machinery  and  trolley  cars. 

While  we  have  all  felt  the  helpful  effects  of  fire,  we  may  have  also 
suffered  from  fire  which  has  not  been  under  control.  Consider 


FIG.  15.  A  French  village  set  on  fire  by  a  German  bomb. 
Copyright  by  George  Grantham  Bain 

the  burning  of  forests,  of  homes,  and  of  large  parts  of  cities.  In 
the  great  Chicago  fire  nearly  one  hundred  thousand  people  were 
made  homeless  and  millions  of  dollars'  worth  of  property  was 


22 


THE  AIR  AND  HOW  WE*USE  IT 


ruined.      In  the  Great  World  War  many  towns  and  cities  were 
wiped  out  of  existence  in  this  way. 

Have  you  ever  considered  the  conditions  necessary  for  a  fire? 
The  problems  which  are  suggested  here  will  show  you  what  hap- 
pens when  a  fire  burns. 


PROBLEMS 
PROBLEM  i :  Is  AN  AIR-SUPPLY  NECESSARY  FOR  BURNING? 

Directions: 

Into  two  wide-mouthed  jars  place  burning  candles.     Over  one  of  the 
jars  place  a  glass  plate.     What  happens? 

(Note  —  Other  substances  besides  candles  may  be  tried.) 

Conclusion: 

Is  an  air-supply  needed  for  burning? 

Questions' 

1.  Why  will  a  burning  match  go  out  if  you  cover  it  with  your  foot? 

2.  Why  should  a  woolen  rug  be  wrapped  around  a  person  whose  clothes 
have  caught  fire? 

3.  Why  must  wood  fires  be  arranged  loosely  in  order  to  burn  well? 

4.  When  should  the  draughts  "of  a  stove  be  opened? 

PROBLEM  2 :  WHICH  OF  THE  GASES  IN  THE  AIR  HELPS  TO  MAKE  THINGS 
BURN? 

Directions: 

Parti  :  Does  oxygen  help  burn- 
ing? Heat  a  large  test-tube  con- 
taining some  potassium  chlorate 
and  manganese  dioxide;  the  gas 
given  off  is  oxygen.  Test  the  gas 
by  putting  a  glowing  splinter 
into  the  top  of  the  tube. 

What  do  you  observe  happens? 
Does  the  gas  burn,  or  does  the 
splinter  burn  ?  Try  other  burning 
substances. 

What  characteristic  of  oxygen 
have  you  demonstrated? 
FIG.  16.  Making  carbon  dioxide.  (Note— This  experiment  may 

also    be  performed   by  using 

oxone.     The  oxone  is  mixed  with  water  and  the  gas  given  off  is 
oxygen.) 


AIR  AND  FIRE 


Part  2:  Does  carbon  dioxide  help  burn- 
ing? Collect  some  carbon  dioxide  in  a  jar 
or  in  a  test-tube.  Carbon  dioxide  can  be 
produced  by  taking  some  calcium  carbonate 
and  adding  some  dilute  hydrochloric  acid. 
This  may  be  run  off  through  a  rubber  tube 
as  shown  in  the  illustration  and  collected 
in  any  convenient  container.  Plunge  a 
lighted  splinter  or  match  into  the  jar  or 
test-tube.  Try  other  burning  substances. 

What  do  you  observe  happens?  Is  carbon 
dioxide  like  oxygen  with  regard  to  burning? 
In  what  respects  is  it  similar  to  oxygen? 

What  properties  of  carbon  dioxide  have 
you  demonstrated? 

Part  3 :  Does  nitrogen  help  burning?  Col- 
lect some  nitrogen  by  displacement  in  water 
by  heating  some  sodium  nitrite.  (Caution! 
Do  not  heat  too  rapidly.)  Put  a  lighted 
splinter  into  the  jar  containing  nitrogen. 
Try  other  burning  substances. 

What  is  the  result?  Does  nitrogen  help 
burning?  Is  nitrogen  like  oxygen  in  regard  to 
burning?  In  what  respects  is  it  like  oxygen? 
Conclusion: 

Which  of  the  gases  which  you  have  tested 
helps  'make  things  burn? 


FIG.  17.  One  way  of  making 
nitrogen,  by  using  up  the  oxygen 
with  burning  phosphorus.  As  the 
oxygen  combines  with  the  phos- 
phorus and  forms  particles  of  a 
soluble  compound  phosphorus  ox- 
ide, the  water  rises  and  takes  the 
place  of  the  oxygen.  The  nitrogen 
made  in  this  way  is  not  pure. 


PROBLEM  3 :  To  FIND  A  TEST  FOR  CARBON  DIOXIDE. 


FIG.  1 8.  A  better  way  of  making  nitro- 
gen, by  heating  sodium  nitrite. 


Directions: 

Make  some  carbon  dioxide  by 
placing  marble,  chips  in  the  bottom 
of  a  flask  and  pouring  in  through 
the  thistle  tube  a  little  dilute  acid  — 
ten  per  cent  sulphuric  or  hydrochlo- 
ric acid. 

Collect  some  of  the  gas  given  off 
in  a  jar  and  pour  in  some  lime 
water. 

Shake  the  jar  and  notice  the  ap- 
pearance of  the  Hme  water. 


Conclusion: 
What  is  the  test  for  carbon  dioxide? 


24  THE  AIR  AND  HOW  WE  USE  IT 

PROBLEM  4:  DOES  THE  AIR  CONTAIN  CARBON  DIOXIDE? 

Directions: 

Let  a  dish  of  lime  water  stand  in  the  room  during  a  period.  What  can 
you  notice  upon  the  surface  at  the  end  of  that  time? 

Let  it  stand  overnight.  Is  there  a  larger  amount  of  material  upon  the 
surface? 

Summary: 

What  does  this  experiment  indicate? 

PROBLEM  5:  WHAT  SUBSTANCES  ARE  PRODUCED  WHEN  A  CANDLE  BURNS? 

Directions: 

Part  i :  Place  a  burning  candle  in  a  covered  jar.  After  the  candle  has 
gone  out  pour  in  some  lime  water.  What  substance  was  formed  by  the 
burning  candle? 

Part  2 :  Above  a  burning  candle  hold  a  cold  piece  of  glass  for  a  moment. 
Examine  the  glass.  Can  you  find  any  drops  of  moisture? 

Conclusion: 
W7hat  are  two  substances  produced  by  the  burning  candle? 

PROBLEM  6:  WHAT  SUBSTANCES  ARE  PRODUCED  WHEN  A  PIECE  OF  WOOD 
BURNS? 

Directions: 

Follow  the  directions  as  given  for  the  candle. 

Conclusion: 
What  are  your  conclusions? 

PROBLEM  7 :  WHAT  SUBSTANCES  ARE  PRODUCED  WHEN  ILLUMINATING  GAS 
BURNS? 

Directions: 

Part  i :  Hold  a  wide-mouthed  jar  over  a  Bunsen  burner  or  a  gas-jet. 
Pour  some  lime  water  into  the  jar.  What  substance  is  present? 

Part  2 :  Find  out  what  forms  on  a  glass  plate  held  over  the  flame.  Can 
you  explain  why  this  is  not  found  in  a  room  where  gas  has  been  burning? 

Conclusion: 
What  are  your  conclusions? 

PROBLEM  8:  WHAT  PROPORTION  OF  THE  AIR  CONSISTS  OF  OXYGEN? 

Directions: 

Fasten  a  candle  to  a  basin  by  letting  a  few  drops  of  melted  wax  fall  upon 
the  basin  and  then  setting  the  candle  on  this  melted  material.  Pour  water 


AIR  AND  FIRE 


into  the  basin.    Light  the  candle  and  carefully  place  an  inverted  cylindrical 

jar  over  the  candle.     Observe  what  happens. 

Questions: 

1.  Why  does  the  candle  go  out? 

2.  Why  does  the  water  rise  in  the  jar? 
(Note  —  Water  can  absorb,   or   soak 

up,  carbon  dioxide.) 

3.  Approximately  how  far  up  the  jar  did 
the  water  rise?    Allowance  will  have  to  be 
made  for  the  space  occupied  by  the  candle 
and  for  the  fact  that  a  few  bubbles  of  air 
escaped  at  the  beginning  of  the  experiment. 

Inference: 

What  is  your  inference  from  this  experi- 
ment? 


PROBLEM  9:  WHAT  is  THE  RELATION  BE- 
TWEEN TEMPERATURE  AND  BURNING? 


FIG.  19.    Burning  a   candle  in 
air.    If  possible,  use  a  jar  instead 
of  a  bottle. 
Directions: 

Part  i :  Place  a  small  piece  of  phosphorus  (Caution !   Do  not  touch !)  on  a 
pan.     Apply  heat  under  the  pan.     What  is  the  result? 

Part  2 :  Put  a  small  amount  of  sulphur  on  a  similar  pan  and  apply  heat  as 
before.     Does  the  sulphur  burn  as  readily  as  the  phosphorus? 

Part  3:  Place  a  small  piece  of  wood  on  a  similar  pan  and  apply  heat 
underneath.     Does  the  wood  burn? 

Part  4 :  From  a  small  piece  of  phosphorus  on  a  pan 
pour  out  a  line  of  sulphur  extending  to  a  splinter  of 
wood.  Gently  heat  the  phosphorus.  What  happens? 
Does  this  experiment  help  you  to  understand  the 
principles  involved  in  the  use  of  matches? 

Summary: 

Do  these  substances  burn  at  the  same  tempera- 
ture? What  uses  are  made  of  this  principle  in  every- 
day life? 

PROBLEM  10:  To  MAKE  AND  USE  A  MODEL  OF  A 

FlRE-EXTINGUISHER. 

FIG.  20.  A  model  of  a      Directions: 

fire-extinguisher.  Arrange  an  apparatus  as  shown  in  the  diagram. 

Upset  the  vial  by  tilting  the  jar.  When  the  gas  is 
escaping  let  the  apparatus  play  upon  a  small  bonfire  made  in  a  pan  upon 
the  demonstration  table. 


26 


THE  AIR  AND  HOW  WE  CSE  IT 


If  the  fire  is  not  too  large  and  the  flow  of  gas  is  good,  what  results  do  you 
obtain?     Explain. 


PROBLEM  1 1 :  To  DEMONSTRATE  THE  USE  OF  A  FIRE-EXTINGUISHER. 

Directions: 

Build  a  bonfire,  not  too  large,  outside  the  school  building.  Take  a  fire- 
extinguisher,  and,  following  directions,  let 
it  play  upon  the  fire.  What  is  the  result? 
Explain. 

A  fire  needs  air.  Any  boy  who  has 
made  a  bonfire  knows  that  in  order  to 
make  it  burn  well  there  must  be  a 
direct  flow  of  air  upon  it  —  in  other 
words,  a  draught.  When  we  wish  to 
increase  the  heat  of  the  fire  in  the 
stove  or  furnace,  we  let  in  more  air 
or  open  the  draught.  When  a  fire  is 
burning  in  the  fireplace  and  we  wish 
to  make  it  burn  more  brightly,  we 
may  use  a  bellows  to  blow  air  upon  it. 
This  principle  of  fanning  the  flame  to 
increase  the  heat  is  used  in  the  huge 
blast  furnaces  in  which  iron  ore  is 
melted.  Such  furnaces,  of  course, 
attain  a  very  high  temperature. 

Why  does  fire  need  a  supply  of 
air?  In  order  to  answer  this  ques- 
tion let  us  inquire:  (i)  What  is  in  the  air  which  makes  fire 
burn?  (2)  What  happens  to  the  air  as  a  result  of  the  burning? 
In  order  to  answer  these  questions  we  must  first  learn  what  air 
is;  in  other  words,  of  what  it  is  composed. 

Composition  of  the  air.  The  air  is  a  mixture  of  invisible  gases 
usually  containing  some  impurities,  such  as  dust.  The  most  im- 
portant gases  which  are  present  in  the  air  are  those  which  are 
called  nitrogen,  oxygen,  carbon  dioxide,  and  water  vapor.  Nitro- 
gen makes  up  about  four  fifths  of  the  air  and  oxygen  about  one 
fifth,  while  carbon  dioxide  composes  about  three  hundred ths  of 


FIG.  21 .  Diagram  of  a  soda-acid  fire- 
extinguisher. 

A ,  ring  handle  F,  acid  line 

B,  screw  cap  G,  bottom 

C,  stopper  H,  handle 

D,  bottle  holder  7,  wire  screen 

E,  filing  line  /,  hose  coupling 

K,  rubber  hose 


AIR  AND  FIRE  27 

one  per  cent.  There  is  also  always  some  water  vapor  present  in 
the  air,  but  this  varies  in  amount  at  different  places  and  at  dif- 
ferent times.  Besides  these  materials,  small  quantities  of  other 
gases  are  also  present.  It  can  readily  be  seen  that  the  air,  in- 
stead of  being  a  simple  gas,  is  really 
a  complex  mixture  of  gases. 

Burning  decreases  the  amount  of 
oxygen  in  the  air.  By  experiments 
you  have  determined  that  oxygen  is 
the  gas  needed  by  fires  to  keep  them 
burning.  You  have  also  discovered 
that  this  gas  is  used  up  when  it  sup- 
ports combustion,  or,  in  other  words, 
makes  things  burn.  Just  what  we  -l^^i^^^-^^'^-^f 
mean  by  saying  that  the  oxygen  is 

<„.?,,  ,    .       •*  FIG.  22.  The  gases  m  the  air. 

used  up      will  be   explained  later. 

For  the  present  we  will  simply  state  that  as  a  result  of  burning, 
the  amount  of  oxygen  in  the  air  is  decreased. 

Extinguishing  fires.  Since  a  fire  depends  upon  a  supply  of 
oxygen,  a  fire  may  be  put  out  by  cutting  off  the  supply  of  oxygen. 
Many  of  the  ordinary  fire-extinguishers  are  made  in  such  a  way 
that  when  operating  they  will  produce  carbon  dioxide  in  sufficient 
quantity  to  smother  the  fire. 

A  very  common  method  of  putting  out  a  small  fire,  as  when  a 
person's  clothing  has  caught  fire,  is  to  throw  a  heavy  blanket  over 
it.  This  usually  produces  the  desired  result  by  shutting  off  the 
oxygen  supply.  If  a  person  with  clothes  on  fire  runs,  the  blaze  is 
apt  to  increase. 

The  reasons  why  an  application  of  water  usually  puts  out  a  fire 
are  that  it  makes  a  coating  which  shuts  off  the  oxygen,  and  that 
it  cools  the  burning  substance.  An  oil  fire  cannot  be  put  out  with 
water  because  water  will  not  make  a  coating  over  oil,  but  instead 
scatters  it  into  parts. 

Burning  often  increases  the  amount  of  carbon  dioxide  and 
water  in  the  air.  Some  of  the  experiments  suggested  at  the  begin- 
ning of  this  project  indicate  that  the  amount  of  carbon  dioxide 
and  water  vapor  is  often  increased  as  a  result  of  burning.  In 


28  THE  AIR  AND  HOW  WE  tSE  IT 

order  to  understand  where  the  carbon  dioxide  and  water  vapor 
come  from  and  under  what  conditions  they  are  formed,  let  us  first 
see  what  kinds  of  matter  such  substances  are. 

Elements  and  compounds.  All  of  the  materials  of  which  our 
world  is  made  are  either  simple  substances  or  else  they  are  com- 
posed of  combinations  of  simple  substances.  One  cannot  tell 
simply  by  looking  at  a  substance  whether  it  is  a  simple  substance 
or  element,  as  these  simple  substances  are  called,  or  whether  it  is 
a  combination  of  elements.  It  is  necessary  to  test  a  substance  in 
various  ways  to  ascertain  its  nature.  There  are  many  such  tests; 
a  study  of  them  is  included  in  the  science  called  Chemistry.  Scien- 
tists tell  us  that  there  are  about  eighty  elements  and  almost  in- 
numerable combinations  and  mixtures  of  these  elements.  As 
far  as  man  has  been  able  to  discover,  elements  consist  of  only  one 
kind  of  material  and  therefore  they  may  be  considered,  as  we  have 
said,  simple  substances.  For  example,  iron  is  called  an  element 
because  up  to  the  present  time  no  one  has  been  able  to  find  any- 
thing else  in  iron  except  iron.  Similarly,  oxygen,  nitrogen,  and 
carbon  are  classed  as  elements. 

Most  of  the  things  around  us,  however,  are  not  elements,  but 
combinations  of  two  or  more  of  these  simple  substances.  These 
combinations  are  called  compounds.  Water  and  carbon  dioxide 
are  examples  of  compounds.  Water  consists  of  two  parts  hydro- 
gen and  one  part  oxygen,  while  carbon  dioxide  consists  of  one 
part  carbon  and  two  parts  oxygen. 

Compounds  are  different  from  the  elements  composing  them. 
One  very  important  thing  to  understand  about  compounds  is  that 
they  are  never  just  like  the  individual  elements  of  which  they  are 
composed.  For  example,  water  is  a  liquid  but  is  made  up  of  two 
invisible  gases,  hydrogen  and  oxygen.  No  one  would  ever  guess 
that  water  can  be  made  by  the  uniting  of  two  gases,  and  yet  this 
is  an  experiment  that  can  very  easily  be  performed  in  a  well- 
equipped  laboratory.  When  a  candle  burns  the  water  that  is 
produced  is  made  by  the  uniting  of  the  hydrogen  which  was  in  the 
candle  with  some  of  the  oxygen  of  the  air. 

Carbon  dioxide  is  a  gas  that  may  readily  be  made  by  causing 
a  solid  substance,  such  as  charcoal,  which  is  carbon,  to  unite  with 


AIR  AND  FIRE 


the  gas,  oxygen.  The  new  gas,  carbon  dioxide,  is  very  different 
from  the  oyxgen  which  helped  to  make  it.  For  example,  car- 
bon dioxide  will  extinguish  a  fire  and  will  turn  lime  water  milky, 
whereas  oxygen  makes  it  possible  for  a  fire  to  burn  and  will  not 
act  upon  lime  water. 

Elements  may  combine  with  each  other.  In  the  production 
of  carbon  dioxide  by  a  burning  candle,  burning  wood,  paper,  etc., 
this  gas  is  formed  as  the  re- 
sult of  the  uniting  of  some 
oxygen  from  the  air  with  some 
carbon  that  was  present  in 
the  burning  material.  These 
two  elements  are  brought  to- 
gether and  made  to  combine 
through  the  influence  of  the 
heat  of  the  flame. 

Another  fact  that  we  should 
notice  at  this  time  is  that 
carbon  dioxide  cannot  be 
made  simply  by  mixing  car- 
bon with  oxygen  any  more 
than  water  can  be  formed  by 
merely  shaking  up  some  oxy- 
gen with  hydrogen.  In  pro- 
ducing these  compounds,  there 
must  be  some  agent  to  make 
the  elements  come  together 
and  unite.  In  the  case  of 


FIG.  23.  Separating  water  into  its  parts  by 
passing  an  electric  current  through  it.     Can 


water,    the    combination    may     you  explain  why  chemists  write  water,  H2O? 

be  effected   by  means  of   an 

electric  current;  in  the  case  of  the  carbon  dioxide,  by  the  agency 
of  heat.  If  elements  are  simply  mixed  together  as  in  the  air, 
where  there  is  a  mixture  but  no  real  union,  the  different  parts 
composing  the  mixture  retain  their  characteristics.  Thus,  it  is 
because  the  oxygen  of  the  air  is  not  really  combined  but  simply 
mixed  with  the  other  gases  that  it  has  the  power  of  making  things 
burn.  If  it  were  truly  united  with  the  nitrogen  and  carbon 
dioxide,  then  the  air  would  not  support  combustion. 


30  THE  AIR  AND  HOW  WE  USE  IT 

Oxidation.  Oxidation  is  the  uniting  of  oxygen  with  some  other 
substance.  We  have  so  far  noted  the  fact  that  oxygen  may  com- 
bine with  carbon  or  with  hydrogen,  but  there  are  also  other  ele- 
ments with  which  it  readily  unites.  Some  of  these  are  iron,  phos- 
phorus, sulphur,  and  magnesium.  One  is \more  apt  to  hear  about 
the  union  of  oxygen  with  carbon  and  hydrogen  than  with  other 
elements  because  all  the  common  kinds  of  fuel  —  coal,  wood,  oil, 
and  gas  contain  these  elements,  carbon  and  hydrogen,  and  when 
they  burn,  the  formation  of  carbon  dioxide  and  water  is  one  of  the 
results. 

Although  a  great  variety  of  substances  may  combine  with 
oxygen,  the  results  of  this  process  are  always  alike  in  two  respects: 
(i)  heat  is  produced,  and  (2)  a  compound  is  made.  This  com- 
pound may  be  a  liquid  such  as  water,  a  solid  such  as  iron  rust, 
or  a  gas  such  as  carbon  dioxide. 

Kinds  of  oxidation.  We  have  just  noted  one  way  in  which  the 
oxidation  process  varies,  namely  with  respect  to  the  kinds  of  ma- 
terials that  may  be  oxidized.  Another  way  in  which  this  process 
varies  depends  upon  the  amount  of  time  that  it  may  take.  Thus, 
oxidation  is  often  spoken  of  as  rapid  or  slow.  Decaying  substances 
such  as  rotting  wood  and  rusting  iron  are  examples  of  slow  oxi- 
dation. Generally,  speaking,  where  light  or  flame  is  visible  the 
oxidation  is  referred  to  as  rapid,  but  where  there  is  only  heat  pro- 
duced whether  perceptible  or  not,  it  is  called  slow.  We  should  not 
forget,  however,  that  in  both  cases  except  for  the  matter  of  light 
the  final  results  are  identical.  Let  us  use  an  illustration. 

Slow  oxidation.  Suppose  that  the  paper  composing  this  page 
should  burn.  It  would  only  take  a  few  seconds  and  quite  a  little 
heat  would  be  given  off.  Now,  let  us  suppose  that  instead  of 
burning  this  page,  we  allow  it  to  undergo  the  usual  slow  process  of 
decay.  After  many  years  nothing  will  be  left  but  ashes.  All  of 
this  time  heat  will  be  given  off,  but  because  the  process  is  so  long 
drawn  out,  it  is  impossible  at  any  one  instant  to  feel  the  heat  com- 
ing from  the  paper.  At  the  end  of  the  process,  after  there  is 
nothing  left  to  be  oxidized,  the  amount  of  heat  produced  will 
exactly  equal  the  amount  which  might  have  been  given  off  had 
the  paper  burned  in  a  few  seconds.  The  quantity  of  ashes  also 


AIR  AND  FIRE  31 

would  be  the  same  in  both  cases.  The  presence  of  water  vapor 
in  the  air  hastens  the  process  of  slow  oxidation.  For  example, 
iron  rusts  and  rocks  and  wood  decay  more  quickly  when  moist. 
If  we  do  not  want  iron  to  rust,  we  prevent  the  air  from  coming  in 
contact  with  it  by  covering  it  with  some  substance  like  paint, 
grease,  stove  polish,  zinc,  tin,  or  nickel. 

Oxidation  helps  us  work.  One  of  the  results  of  oxidation  is  the 
production  of  energy.  By  energy,  we  mean  the  power  to  do  work. 
An  illustration  will  make  our  meaning  clear.  The  steam  engine 
depends  upon  the  burning  of  fuel  for  its  power  or  energy.  The 
fire  in  the  fire-box  causes  the  water  to  change  into  steam  in  the 
boiler;  the  expansion  of  the  water  into  steam  is  used  to  make  the 
piston  move,  which  in  turn  makes  the  wheels  revolve.  Thus  in  the 
case  of  the  steam  engine,  the  cause  of  the  activity  can  quite  read- 
ily be  traced  back  to  oxidation.  As  we  shall  find  in  the  next  chap- 
ter, this  is  not  only  true  among  non-living  things  such  as  machines, 
but  it  is  also  true  that  the  activities  of  all  plants  and  animals  are 
directly  dependent  upon  the  slow  oxidation  which  occurs  within 
them. 

Matches.  Although  carbon  unites  with  oxygen  quite  readily, 
there  are  some  things  which  unite  with  it  even  more  rapidly  and 
at  lower  temperatures.  One  of  the  primitive  ways  of  starting  a 
fire  was  to  rub  pieces  of  wood  together  until  the  friction  produced 
enough  heat  to  make  a  spark  from  which  a  fire  might  be  kindled. 
Another  method  that  was  until  recent  times  quite  generally  used 
by  every  one  was  to  strike  flint,  a  kind  of  hard  rock,  upon  steel, 
thus  producing  a  spark.  In  the  seventeenth  century  it  was  found 
that  sulphur  could  be  used  to  save  time  in  making  fires:  (i)  be- 
cause it  ignites  at  a  lower  temperature  than  wood,  and  (2)  because 
it  produces  enough  heat  when  burning  to  ignite  wood.  It  was 
not  until  1823,  however,  that  the  "parlor  match"  was  manu- 
factured. The  matches  of  to-day  usually  contain  phosphorus. 
This  element  unites  with  oxygen  at  a  considerably  lower  tempera- 
ture than  sulphur,  so  that  its  use  helps  to  start  the  oxidation  when 
just  a  little  heat  is  generated  by  friction.  All  that  is  necessary  to 
ignite  such  matches  is  to  "  strike  "  them  upon  something.  The 
friction  produces  enough  heat  to  cause  the  oxidation  of  the  phos- 


32  THE  AIR  AND  HOW  WE  USE  IT 

phorus  and  the  heat  thus  produced  in  turn  starts  the  sulphur 
burning  and  finally  the  wood  itself. 

Ordinary  friction  matches  of  to-day  are  tipped  with  a  mixture 
of  yellow  phosphorus,  powdered  glass,  and  glue  to  hold  the  mass 
together.  When  such  matches  are  rubbed  on  a  rough  surface,  the 
heat  of  friction  heats  the  phosphorus  to  its  kindling  temperature. 

Phosphorus,  however,  is  deadly  poison  so  that  some  countries 
have  prohibited  its  use  in  the  manufacture  of  matches.  In  the 
so-called  "safety-matches,"  there  is  no  phosphorus  in  the  head, 
but  the  material  upon  which  they  must  be  struck  in  order  to  be 
ignited  contains  it  in  a  modified  form.  The  invention  of  matches 
has  resulted  in  a  great  saving  of  time  and  labor. 

Matter  may  change  its  form  but  cannot  be  destroyed.  The 
world  in  which  we  live  and  the  things  in  it  are  constantly  chang- 
ing. Nothing  remains  just  as  it  is  or  has  been ;  not  even  the  hard- 
est rocks  on  the  surface  of  the  earth  are  everlasting.  The  most 
common  cause  of  changes  in  matter  is  this  process  which  we  have 
been  studying  —  oxidation.  Let  us  very  briefly  consider  some 
of  the  broad,  general  ways  in  which  our  knowledge  of  oxidation 
ought  to  help  us  better  to  understand  our  world. 

Suppose  some  uninformed  person  had  performed  the  experi- 
ments referred  to  in  the  beginning  of  this  project.  He  would  be 
very  likely  to  come  to  wrong  conclusions  about  them.  He  might 
suppose,  for  instance,  that  when  oxygen  is  used  to  help  something 
burn,  it  actually  goes  out  of  existence.  We  know  that  this  is  not 
true.  We  know  that  oxygen  under  those  conditions  enters  into 
what  is  called  a  "chemical  combination"  with  another  element, 
thus  forming  a  compound.  Here  is  a  case  where  apparently  some- 
thing goes  out  of  existence,  but  does  not  actually  do  so.  It  fur- 
nishes an  illustration  of  one  of  the  most  fundamental  laws  of  na- 
ture which  is  so  universally  true  that  scientists  have  formulated 
it  into  a  principle  or  law  called  the  law  of  the  indestructibility  of 
matter.  This  law  states,  that  although  matter  may  be  made  to 
change  its  form,  it  cannot  really  be  destroyed.  For  instance,  a  house 
may  be  burned  down.  Its  form  may  be  destroyed,  but  the  ele- 
ments of  which  the  house  was  composed  are  still  in  existence. 
Most  of  them  have  gone  to  help  form  invisible  gases. 


AIR  AND  FIRE  33 

Matter  cannot  be  created.  Another  wrong  conclusion  that 
night  be  made  from  our  experiments  is  that  carbon  dioxide  comes 
into  existence  from  nothing.  We  have  seen  that  this  is  not  true. 
Just  as  matter  cannot  really  be  made  to  go  out  of  existence,  so  it  is 
likewise  true  that  matter  cannot  be  made  out  of  nothing.  To  put 
these  ideas  into  slightly  different  language,  it  is  true  that  as  far 
as  man's  knowledge  extends,  there  is  just  as  much  matter  in  the 
universe  to-day  as  there  always  has  been,  and  as  far  as  we  can  see 
there  will  never  be  any  more  or  any  less  than  there  is  now. 

INDIVIDUAL  PROJECTS 

Working  projects: 

1.  Make  a  collection  of  the  forms  of  carbon.     (See  a  chemistry  textbook.) 

2.  Use  a  fire-extinguisher.     Let  a  pupil  or  a  group  of  pupils  make  a  bon- 
fire near  the  school  and  then  use  a  fire-extinguisher  to  put  it  out.     Refill 
the  extinguisher. 

3.  Additional  experiments  with  oxygen.     (See  a  chemistry  textbook.) 

4.  Experiments  with  sulphur.     (See  a  chemistry  textbook.) 

5.  Experiments  with  phosphorus.     (See  a  chemistry  textbook.) 

6.  A  Boy  or  Girl  Scout  may  demonstrate  how  to  make  a  fire  without  matches. 

Reports: 

1.  How  matches  are  made. 

The  Book  of  Wonders.     Presbrey  Syndicate,  New  York. 

Sweden  and  Safety  Matches.     N.  B.  Allen.     Ginn  &  Co. 

Great  Inventions  and  Discoveries.     C.  Piercy.     Chas.  E.  Merrill  &  Co. 

Makers  of  Many  Things.     E.  M.  Tappan.     Houghton  Mifflin  Co. 

Stories  of  Useful  Inventions.     S.  E.  Forman.  Century  Co. 

2.  History  of  firemaking. 

The  Origins  of  Inventions.    O.  Tv  Mason.     Chas.  Scribner  s  Sons. 
Stories  of  Useful  Inventions.    C.  Piercy.    Chas.  E.  Merrill  &  Co. 

3.  The  work  of  a  fire  department. 

Visit  the  fire  department  headquarters  in  your  community  and  find 

out  as  much  as  you  can  about  the  equipment,  etc. 
Careers  of  Danger  and  Daring.     C.  Moffett.     Century  Co. 
The  Romance  of  Modern  Mechanism.    A.  Williams.    J .  B.  Lippmcott  Co. 
Town  and  City.     F.  G.  Jewett.     Ginn  &  Co. 

4.  Interesting  facts  about  oxygen.     (See  a  chemistry  textbook.) 

5.  Interesting  facts  about  carbon  dioxide.     (See  a  chemistry  textbook.) 

6.  Interesting  facts  about  carbon.     (See  a  chemistry  textbook.) 

7.  Interesting  facts  about  nitrogen.     Scientific  American  Supplement,  July 

22,  1916. 


PROJECT  III 
AIR  AND  BREATHING 

All  plants  and  animals  breathe.  Did  you  ever  think  what  a  re- 
markable thing  it  is  that  as  long  as  we  live,  whether  awake  or 
asleep,  air  is  made  to  pass  into  and  out  of  our  bodies  about  six- 
teen times  every  minute?  What  a  wonderful  adjustment  our 
bodies  show  in  that  we  do  not  have  to  think  about  breathing  in 
order  to  perform  this  extremely  necessary  act! 

Every  one  knows  that  one  way  of  telling  whether  an  animal  is 
alive  or  dead  is  to  find  out  whether  it  is  breathing.  All  plants 
that  are  actively  alive  breathe.  As  we  study  this  project  we  shall 
want  to  find  out  about  the  wonderful  arrangements  nature  pro- 
vides in  order  that  breathing  may  be  carried  on.  We  shall  study 
especially  about  the  breathing  organs  of  the  human  body. 

Problems  1-4,  8,  9,  12,  and  13  all  deal  with  the  way  we  breathe. 
How  some  animals  breathe  you  will  learn  in  problems  5  and  10; 
how  some  plants  breathe,  in  problems  6,  7,  and  n.  To  learn  how 
to  restore  breathing  in  a  person  who  is  near  death  from  drowning 
or  suffocation,  perform  problem  14. 

Besides  studying  what  this  book  contains  about  this  most  es- 
sential of  life  processes,  you  will  wish  to  learn  what  some  of  the 
special  sciences  teach  about  the  breathing  of  other  creatures. 
Biology,  the  study  of  life,  includes  the  study  of  all  living  creatures, 
—  plants,  animals,  and  man.  Consult  the  individual  projects  and 
the  references. 

PROBLEMS 
PROBLEM  i :  How  DOES  EXERCISE  AFFECT  THE  RATE  OF  BREATHING? 

Directions: 

First  determine  the  rate  of  breathing  while  sitting  quietly  without  hav- 
ing taken  any  exercise  immediately  preceding  the  experiment.  Count  the 
number  of  breaths  taken  in  a  minute  while  breathing  naturally.  Exercise 
vigorously  for  a  few  minutes  and  then  again  count  the  number  of  breaths. 


AIR  AND  BREATHING  35 

Conclusion: 
How  does  exercise  affect  your  rate  of.  breathing? 

PROBLEM  2:  WHAT  is  THE  TEMPERATURE  OF  THE  HUMAN  BODY? 

Directions: 

Place  a  physician's  thermometer  under  the  tongue  and  let  it  remain 
there  for  two  or  three  minutes.  Then  examine  it  to  find  to  what  point  the 
mercury  has  risen. 

Questions: 

1.  What  is  the  temperature  under  the  tongue? 

2.  Is  this  higher  or  lower  than  the  temperature  of  the  air  in  the  room? 
If  higher,  how  do  you  account  for  the  difference? 

PROBLEM  3:  Is  CARBON  DIOXIDE  GIVEN  OFF  IN  BREATHING? 

Directions: 

Part  i.  Breathe  for  a  few  moments  through  a  tube  into  a  small  quantity 
of  lime  water.  Examine  the  lime  water. 

Questions: 

What  is  indicated  by  the  result  of  this  experiment?  Does  it  prove  that 
the  body  gives  off  carbon  dioxide? 

Part  2.  By  means  of  an  atomizer  force  air  about  equal  in  amount  to  that 
which  was  exhaled  through  a  similar  quantity  of  lime  water.  Compare  the 
appearance  of  this  lime  water  with  the  appearance  of  the  lime  water 
through  which  the  breath  has  been  forced. 

Questions: 

Is  there  any  difference  in  the  appearance  of  the  lime  water  treated  in 
the  ways  indicated?  Which  is  the  more  milky? 

Conclusion: 

Are  you  justified  in  concluding  that  the  body  gives  off  carbon  dioxide? 
Explain. 

PROBLEM  4 :  Is  WATER  VAPOR  GIVEN  OFF  IN  BREATHING? 

Directions: 

Breathe  upon  a  cold  piece  of  glass.  What  is  formed  upon  the  glass? 
Where  did  it  come  from? 

Conclusion: 
What  is  your  conclusion? 

PROBLEM  5 :  DOES  A  FISH  GIVE  OFF  CARBON  DIOXIDE? 

Directions: 
For  a  few  moments  place  a  fish  in  a  small  quantity  of  lime  water. 


THE  AIR  AND  HOW  WE  USE  IT 


Does  the  appearance  of  the  lime  water  change?  If  so,  what  does  it 
prove? 

Question: 

In  what  way  is  a  fish's  breathing  similar  to  a  person's? 

PROBLEM  6:  Do  GERMINATING  SEEDS  USE  OXYGEN? 

Directions: 

Soak  twenty  or  thirty  seeds,  such  as  kidney  beans  or  peas,  overnight. 
Place  them  in  a  stoppered  flask  with  a  little  water.  The  water  should  not 
cover  the  seeds.  Place  the  flask  in  a  moderately  warm  place  for  three  or 
four  days. 

Remove  the  stopper  from  the  flask  and  insert  a  burning  splinter.  What 
happens? 

Questions: 

1.  What  does  the  result  of  the  experiment  prove? 

2.  Do  plants,  when  they  breathe,  use  the  same  gas  that  animals  use? 

PROBLEM  7:  Do  GERMINATING  SEEDS  GIVE  OFF  CARBON  DIOXIDE? 

Directions: 

Start  twenty  or  thirty  seeds  —  kidney  beans  or  peas  are  satisfactory  — 

germinating  in  sawdust  or  upon  moist  blotting-paper.     Transfer  them  to 

a  flask  with  a  stopper  having  two 
holes.  Into  one  of  the  holes  place 
a  bent  glass  tube  with  an  atom- 
izer attached.  Into  the  other  hole 
have  another  bent  tube  inserted. 
Remove  the  stopper  from  the 
flask  and  let  the  seeds  continue  to 
germinate  for  two  or  three  days. 

Insert  the  stopper  with  the  at- 
tachments into  the  mouth  of  the 
flask,  as  shown  in  the  diagram,  and 
let  the  apparatus  stand  for  a  half- 
hour.  Squeeze  the  bulb  of  the 
atomizer,  thus  forcing  air  in  and 

out  of  the  flask.     Let  the  air  which  comes  out  pass  through  lime  water. 

Questions: 

1.  Is  the  lime  water  affected  by  the  air  which  was  in  the  flask? 

2.  What  do  you  conclude  from  the  results  of  this  experiment? 

3.  Do  plants  in  breathing  give  off  the  same  gas  that  animals  do? 

4.  It  has  been  found  that  seeds,  even  when  not  germinating,  give  off 
small  quantities  of  carbon  dioxide.    What  is  the  meaning  of  this  fact? 


FIG.  24.  An  experiment  to  show  what  sprout- 
ing seeds  breathe  out. 


AIR  AND  BREATHING 


37 


PROBLEM  8:  WHAT  ARE  CELLS? 
Directions: 

With  a  clean  scalpel  gently  scrape  off  some  of  the  cells  from  the  inside 
lining  of  the  cheek.  Also  scrape  off  the  thin  skin  of  a  small  portion  of  an 
onion. 

I   Examine  by  means  of  the  compound  microscope.     Do  the  cells  vary  in 
shape?    How  many  dimensions  has  a  cell?    How  many  does  it  appear  to 

have?    Why?    In  some  of  the  cells  

can  you  see  the  nucleus,  a  part  usu- 
ally near  the  center  of  the  cell  and 
darker  than  the  rest?  Describe  the 
cell  wall  around  each  onion  cell.  Can 
you  see  the  colorless  living  matter 
inside  the  cells? 

Stain  some  of  the  specimens  with 


iodine  and  examine  again.    Can  you 
now  see  the  nucleus  more  distinctly? 

Summary: 

'i.  What  are  the  main  parts  .of  a 
cell? 

2.  Why  are  the  cells  called  units 
of  structure  of  living  things? 

PROBLEM  9:  To  SEE  THE  CELLS  IN 
THE  BLOOD. 


•£-N 


FIG.  25.  A  thin  piece  of  onion  skin  stained 
with  iodine  and  placed  under  the  microscope. 

N,  nucleus;  P,  protoplasm;  W,  cell  wall. 


Directions: 

A  blood  smear  may  be  made  as 
follows:    Prick  the  finger  with   a 

sterilized  needle.  It  is  unnecessary  to  secure  even  as  much  as  a  single 
drop  of  blood.  Put  the  blood  upon  one  end  of  a  slide.  By  using  another 
slide  make  a  thin  line  of  blood  and  then  proceed  to  spread  out  this  blood  by 
drawing  the  last  mentioned  slide  over  the  one  upon  which  the  blood  was 
placed. 

The  slide  thus  prepared  will  dry  immediately  and  needs  no  cover-glass. 
Examine  under  the  high  power  microscope.  If  the  slide  was  properly 
made  it  will  be  possible  to  find  places  where  individual  cells  may  be 
examined. 

(If  frog's  blood  is  available,  it  may  be  substituted  for  human  blood  or 
the  two  may  be  used  for  purposes  of  comparison.) 

Summary: 

i.  Can  you  make  out  the  shape  of  the  red  corpuscles?  Describe.  Are 
the  red  corpuscles  red  when  examined  singly  or  in  small  groups?  Can 
you  explain  why  this  is  so? 


THE  AIR  AND  HOW  WE  USE  IT 


2.  Can  you  see  any  white  corpuscles? 
pearance  with  the  red  cells. 


Compare  them  in  size  and  ap- 


PROBLEM 10:  How  DOES  A  FISH  BREATHE? 


FIG.  26.  Breathing  organs  of  a  fish. 
h,  heart;  a,  artery;  v,  vein;  g,  gills. 


Directions: 

Watch  the  mouth  of  a  fish  in  the 
aquarium.  Does  it  stay  closed  or 
does  it  open  and  shut  quite  fre- 
quently? 

Can  you  see  the  little  flaps  or 
gill -covers  at  the  side  of  the  head? 
Does  their  movement  have  any 
connection  with  the  movement  of 
the  mouth?  (See  diagram.) 

Examine  the  gills  by  lifting  the 
gill-covers.     What  color  are  they? 
Does    this    indicate    what    they 
probably  contain? 
Summary: 

Write  in  your  notebook  an  ac- 
count of  the  breathing  movements 
of  a  fish,  illustrating  with  drawings. 


PROBLEM  1 1 :  How  DOES  A  PLANT  BREATHE? 

Directions: 

Peel  off  a  little  of  the  under  surface  or  epidermis  of  a  Boston  fern  or  leaf 
from  a  plant  belonging  to  the  lily  family. 

Place  the  transparent  piece  of  epidermis  on  a  clean  glass  slide.  Add  a  drop 
of  water  and  a  cover-glass,  and  examine  with  the  compound  microscope. 

Find  oval  spots,  scattered  over  the  surface.  Can  you  see  that  each  spot 
is  not  one  cell,  but  is  really  a  hole  in  the  skin  with  two  bean-shaped  cells 
around  it?  The  hole  is  the  breathing  pore.  The  two  cells  are  called 
guard  cells,  because  they  guard  the  opening. 

Summary: 

Explain  how  air  can  get  in  and  out  through  the  surface  of  a  leaf. 

Drawing  (optional): 

Make  a  careful  labeled  drawing,  showing  epidermis  cells,  cell  walls, 
breathing  pores,  and  guard  cells. 

PROBLEM  12:  How  DOES  A  PERSON  BREATHE? 

Directions: 

Part  i.  The  parts  of  the  breathing  tract.  Through  what  passageways 
may  the  air  enter  and  leave  the  body? 


AIR  AND  BREATHING 


39 


By  means  of  the  diagram 
trace  the  course  taken  by 
the  air  on  its  way  to  and 
from  the  lungs. 

Part  2.  The  cause  of  the 
breathing  movements. 

(Note — Although  the 
muscles  attached  to  the 
ribs  help  to  produce 
the  breathing  motions, 
the  large  muscle  —  the 
diaphragm  —  separat- 
ing the  chest  cavity 
from  the  abdominal 
cavity,  does  most  of  the 
work.) 

In  order  to  demonstrate 
the  action  of  the  diaphragm 
construct  an  apparatus  as 
shown  in  the  figure. 

A  bell  jar  with  an  open- 
ing at  the  top  has  rubber 
sheeting  fastened  securely 
around  the  larger  opening. 
A  rubber  stopper  with  one 
hole  has  a  Y-shaped  glass  tube 


FIG.  28.  An  apparatus  to  show  the  action  of 
the  diaphragm. 


FIG.  27.  The  breathing  organs. 
(From  Woods  Hutchinson's  Handbook  of  Health.) 

inserted  with  small  toy  balloons  fastened 
to  it,  as  shown  in  the  figure.  By 
pulling  the  rubber  sheeting  down 
and  then  pushing  it  in,  the  toy 
balloons  can  be  made  to  expand 
and  contract.  Explain. 

Summary: 

What  part  of  the  apparatus  cor- 
responds to  the  wind-pipe  or  tra- 
chea? the  bronchial  tubes?  the 
lungs?  the  diaphragm?  the  walls 
of  the  chest  cavity? 

Questions: 

1.  In  what  respects  is  the  ap- 
paratus different  from  the  human 
breathing  apparatus? 

2.  In  what  respects  is  it  simi- 
lar? 


40  THE  AIR  AND  HOW  WE  "USE  IT 

PROBLEM  13:  WHAT  is  MY  CHEST  EXPANSION? 

Directions; 

By  using  a  respiration  apparatus  determine  the  number  of  cubic  inches 
that  represents  your  chest  expansion. 

Summary; 

Is  your  chest  expansion  above  or  below  the  average  in  your  class? 
What  can  you  do  to  increase  your  chest  capacity? 

PROBLEM  14:  How  is  ARTIFICIAL  RESPIRATION  PRODUCED? 

Directions: 

Let  a  pupil  lie  upon  his  stomach  with  head  turned  to  one  side.  The 
teacher  should  then  place  the  palms  of  his  hands  upon  the  lower  ribs.  In 
order  to  produce  an  exhalation  the  instructor  should  bear  his  weight  down 
upon  the  ribs.  In  the  case  of  a  person  who  is  unconscious,  releasing  this 
pressure  will  allow  the  chest  cavity  to  become  larger  with  the  result  that 
air  will  tend  to  enter  the  lungs.  This  should  be  repeated  about  sixteen 
times  a  minute.  Why? 

Questions; 

1.  What  are  some  of  the  conditions  under  which  artificial  respiration 
should  be  given? 

2.  In  case  of  drowning  what  should  be  done  before  artificial  respiration 
is  applied? 

3.  What  instrument  may  be  used  to  produce  artificial  respiration? 

Activity  in  relation  to  the  rate  of  breathing.  There  are  some 
living  things  that  are  inactive  during  certain  seasons.  Bears  and 
snakes  are  examples  of  animals  that  hibernate  or  go  into  a  kind  of 
sleep  during  part  of  the  winter.  Still  lower  forms  of  plants  and 
animals  may  actually  be  frozen  and  then  afterwards  thawed  out 
to  become  actively  alive  again.  Such  living  things  during  their 
periods  of  inactivity  breathe  very  little  and  some  of  them  at  times 
probably  not  at  all.  We  can  conclude,  therefore,  that  there  is 
a  connection  between  the  rate  of  breathing  and  the  amount  of 
activity  of  the  living  being.  When  there  is  an  extra  amount 
of  activity  the  breathing  becomes  faster.  When  you  run  you 
breathe  faster  and  with  deeper  gasps  than  when  you  walk. 

Heat  production  in  relation  to  the  rate  of  breathing.  Rapid 
breathing  and  an  increased  production  of  heat  generally  go  to- 
gether. By  using  a  physician's  thermometer  you  will  find  that 
your  body  temperature  under  the  tongue  is  about  ninety-eight 


AIR  AND  BREATHING  41 

and  three-fifths  degrees,  Fahrenheit.  This  is  usually  consider- 
ably warmer  than  the  surrounding  air.  What  do  you  suppose 
causes  this  body  heat?  As  has  already  been  stated  (see  page  31), 
oxidation  is  going  on  in  the  living  body  and  this  results  in  the 
high  body  temperature.  What  is  true  of  the  human  body  is  also 
true  of  other  living  things,  al- 
though most  animals  and  all 
plants  have  not  as  high  a 
temperature  as  that  of  the 
human  body. 

Air  that  we  breathe  in. 
We  breathe  the  air  that  sur- 
rounds us,  whatever  it  may 
be.  Usually,  the  air  consists 
of  about  eighty  per  cent  ni- 
trogen, twenty  per  cent  oxy- 
gen, and  three  hundred ths  of 
one  per  cent  carbon  dioxide. 
(See  page  27.)  These  figures 
do  not  include  the  water  va- 
por which  is  also  always  pres- 
ent but  in  varying  quantities. 

Air  that  we  breathe  out. 
Our  problems  have  shown  that 
the  air  breathed  out  is  dif- 
ferent in  two  respects  from  the 
outside  air.  It  contains  more 
carbon  dioxide  and  water  va- 
por. It  has  also  been  de- 
prived of  some  of  its  oxygen. 
It  still  contains  about  eighty 
per  cent  nitrogen.  Experi- 
ments show  that  the  oxygen 
has  been  decreased  from  ap- 
proximately twenty  per  cent  to  about  sixteen  per  cent,  while 
the  carbon  dioxide  has  increased  from  considerably  less  than  one 
per  cent  to  about  four  per  cent.  At  the  same  time  there  has 
been  a  slight  increase  in  the  amount  of  water  vapor. 


FIG.  29.  Breathing  organs  of  a  plant. 
A,  the  under  surface  of  a  geranium  leaf 
that  has  been  well  watered.  B,  the  under 
surface  of  a  geranium  leaf  from  a  plant  that 
has  suffered  drought.  C,  enlarged  view  of  a 
stoma  made  of  an  opening,  S,  and  two  guard 
cells,  G.  D,  side  view  of  a  stoma. 


42  THE  AIR  AND  HOW  WE  USE  IT 

Breathing  of  plants.  Plants  as  well  as  animals  breathe.  They 
make  use  of  the  same  gas  that  animals  use  and  also  give  off  the 
same  gas  that  animals  give  off.  Perhaps  you  have  heard  the  op- 
posite of  this;  namely,  that  when  plants  breathe  they  take  in  car- 
bon dioxide  and  exhale  oxygen.  No  plant  ever  did  this  as  a  re- 
sult of  breathing.  Green  plants,  however,  take  in  carbon  dioxide 
and  give  off  oxygen  as  the  result  of  an  entirely  different  process, 
which  we  shall  learn  about  later.  Let  us  clearly  recognize  these 
two  facts,  and  not  confuse  this  other  process  with  breathing: 
(i)  All  living  things  breathe;  (2)  when  they  breathe,  all  take  in 
oxygen  and  give  off  carbon  dioxide. 

The  human  body  a  machine.  A  machine  is  a  device  for  doing 
work.  A  healthy  person  can  accomplish  useful  work.  Therefore, 
in  a  very  true  sense  the  human  body  is  a  machine.  One  of  the 
most  important  parts  of  this  machine  is  that  which  has  to  do  with 
breathing.  If  the  breathing  organs  refuse  to  work,  the  machine 
itself  is  useless.  Many  owners  of  automobiles  know  how  to  run 
their  machines  until  an  accident  happens,  and  then,  because  they 
do  not  understand  the  structure  and  working  of  the  parts,  they 
are  helpless  to  repair  the  wrong.  Perhaps  it  is  a  very  simple 
thing  that  a  little  knowledge  rightly  applied  would  adjust  in  a 
moment.  A  similar  state  of  affairs  holds  true  regarding  the 
human  body  except  that  instead  of  relatively  only  a  few  people 
owning  this  machine,  every  one  has  been  given  a  model  to  look 
after.  Yet  some  people  never  take  the  trouble  to  study  even  a 
little  about  the  structure  and  action  of  the  most  vitally  important 
parts  of  their  own  bodies.  Consequently,  breakdowns  in  the  form 
of  sicknesses  are  apt  to  occur,  which  a  little  applied  knowledge 
might  in  many  cases  easily  have  prevented.  A  large  proportion 
of  sickness  is  due  to  ignorance.  A  knowledge  of  physiology,  the 
study  of  the  use  of  the  different  parts  of  the  body,  together  with 
a  knowledge  of  hygiene,  the  study  of  its  care,  are  fundamentally 
important.  Every  boy  and  girl  ought  to  know  something  about 
the  structure  of  the  body,  just  as  one  needs  to  know  about  the 
structure  of  an  automobile  before  he  can  intelligently  take  care 
of  it. 

Cells  —  the  building  units  of  a  living  body.    When  we  look  at 


AIR  AND  BREATHING 


43 


.  a  brick  wall  from  a  distance,  we  can  see  the  wall,  but  not  the 
separate  bricks.     As  we  approach  it,  the  separate  units  that  make 
up  the  wall  can  be  seen.     A 
living  body  may  be  compared 
to  a  brick  wall.    We  cannot 
see  the  separate  units,  the  cells, 
unless  we  magnify  them  with 
a  microscope.      Then  we  can 
see  their  marvelous  and  beau- 
tiful structure. 

The  parts  of  a  cell.  The 
most  important  part  of  any 
cell  is  the  living  part,  which 
seems  to  be  a  kind  of  jelly,  with 
little  granules  and  threads. 
The  name  given  to  this  living 
matter  is  protoplasm.  Cells 
are  of  hundreds  of  different 
shapes  and  sizes.  Plant  cells 
have  a  wall  around  them, 
which  is  not  itself  alive.  The 
material  of  the  wall  is  like 
cotton ;  indeed,  each  little  fiber 
of  cotton  is  a  cell  wall.  This 
cell  wall  is  made  of  cellulose, 
a  substance  manufactured  by 
the  living  protoplasm. 

In  almost  all  cells  there  is  a 


6 


FIG.  30.  (i)  Five-sided  liver  cells.  (2)  Nerve 
cell  with  long  sheathed  elongation.  (3)  Fat 
cells.  The  protoplasm  and  nucleus  have  been 
pushed  to  one  side  by  the  fat  deposited  in 
the  cell.  (4)  Muscle  cell  from  the  stomach. 

(5)  Bone  cells,  surrounded  by  bony  deposit. 

(6)  Striated  muscle  cells.    (7)  Cells  in  connec- 
tive tissue.   The  cells  give  out  a  jelly-like  mass 
which  hardens  to  a  strong  elastic  mass. 


part  called  the  nucleus.    The 

nucleus  is  the  part  of  the  cell  which  regulates  the  life  activities 

of  the  cell. 

How  many  cells  a  living  body  contains.  Some  animals  are  so 
simple  and  tiny  that  they  consist  of  only  one  cell.  Stagnant 
water  may  have  millions  of  such  little  animals,  all  busily  living 
their  lives  together,  eating,  breathing,  and  moving.  Many 
plants,  too,  consist  of  only  one  cell;  for  example,  yeast  and  bacte- 
ria. Most  plants  and  animals,  however,  contain  many  thousands 


44 


THE  AIR  AND  HOW  WE  USE  IT 


of  cells.     It  is  impossible  to  estimate  the  millions  that  are  in  a 
human  body,  every  living  part  of  which  is  made  of  cells. 

Tissues  and  organs.  When  a  number  of  cells  of  the  same  kind 
do  the  same  work,  we  call  the  mass  a  tissue.  We  have  muscle 
tissue,  for  example,  all  made  of  muscle 
cells;  we  have  bone  tissue,  blood  tissue, 
brain  tissue,  and  so  on.  When- a  number 
of  tissues  are  combined  to  do  a  certain 
kind  of  work,  we  call  the  mass  an  organ. 
The  hand  is  an  organ,  with  its  own  kind 
of  work  to  do.  It  is  made  of  many  tissues 
-  blood,  bone,  muscle,  tendon,  skin,  and 
nerves. 

Cells  in  the  blood.  Perhaps  you  have 
always  thought  of  the  blood  as  a  red  liquid. 
Is  it  always  red?  Can  you  see  the  veins 
in  the  back  of  your  hand?  What  color  is 
the  blood  in  them? 

When  you  look  at  a  drop  of  blood 
through  a  microscope,  you  can  see  that 
there  are  solid  parts  in  it,  both  red  and 
white,  called  corpuscles,  or  "little  bodies." 
The  red  corpuscles  are  the  most  abundant 
—  tiny  discs,  often  piled  one  on  top  of  an- 
other. Strangely  enough,  they  are  not  red 
at  all,  but  a  kind  of  straw  color,  unless  many 
of  them  are  together,  when  the  color  looks 
red.  They  are  floating  in  the  liquid  part  of 
the  blood,  which  is  colorless.  You  may  think 
of  each  little  corpuscle  as  a  tiny  boat  float- 
ing in  the  blood  stream,  with  a  load  aboard 
it.  The  load  is  oxygen.  The  boats  are 
loaded  in  the  lungs  where  a  fresh  supply  of 
oxygen  is  always  coming  in.  Then  they  pass 
through  the  blood  vessels  to  the  cells  all  over  the  body,  giving  up 
their  load  of  oxygen  where  it  is  needed.  There  are  approximately 
five  million  of  these  red  corpuscles  in  every  drop  of  blood. 


FIG.  31.  Cells  from  the 
lining  of  the  mouth  and 
throat  bearing  cilia  (C) .  Cer- 
tain cells  (M)  produce  sticky 
mucus  (5),  which  coats  the 
lining  of  the  throat  and 
gathers  dust  and  bacteria  as 
it  is  forced  up  by  the  beating 
of  the  tiny  cilia. 


FIG.  32.  A  drop  of  blood 
seen  through  the  micro- 
scope showing  red  disk- 
like  bodies,  the  red  cor- 
puscles, and  the  white  cor- 
puscles. These  cells  float 
in  a  colorless  fluid  called 
the  plasma. 


AIR  AND  BREATHING 


45 


The  breathing  organs  of  the  human  body.  You  know  that  you 
breathe  by  means  of  lungs.  If  you  could  see  your  own  lungs  you 
would  find  that  they  are  thin-walled  sacs,  pink  in  color.  Their 
color  is  due  to  the  fact  that  they  are  supplied  with  thousands  of 
tiny  blood  vessels  through  the  walls  of  which  oxygen  is  constantly 
entering. 

As  you  -will  see  by  examining  the  illustration  on  page  39,  the 
air  entering  the  body  passes  through  the  mouth  or  nose  to  the 
throat   and    then   down    a 
tube,    the    wind-pipe,    into 
the  lungs. 

Why  the  air  passes  into 
and  out  of  the  lungs.  There 
is  nothing  in  the  mouth  or 
nose  that  is  able  either  to 
suck  air  in  or  to  expel  it. 
If  we  want  to  find  an  expla- 
nation for  the  breathing  mo- 
tions we  must  look  farther 
than  these  parts  of  the  body. 
We  shall  have  to  learn  some- 
thing about  a  large  muscle 
which  is  flattened  and  dome- 
shaped  and  which  stretches 
across  the  body  from  front 
to  back  and  from  side  to 
side  just  below  the  lungs. 
This  muscle  is  called  the 
diaphragm.  The  diaphragm 
divides  the  body  cavity  into 
two  parts,  the  upper  called 

the  chest  cavity  and  the  lower,  the  abdomen.  The  lungs,  which 
are  in  the  chest  cavity,  are  composed  of  thin,  elastic  tissues.  They 
completely  fill  the  chest  cavity,  except  for  the  space  occupied  by 
the  heart,  some  blood  vessels,  and  the  food  tube  leading  from 
the  mouth  to  the  stomach.  The  diaphragm,  like  other  muscles, 
can  contract.  As  a  result  of  its  contraction  the  chest  cavity  is 


-X- 


FIG.  33.  Why  the  chest  cavity  is  enlarged. 

s,  the  breastbone  r,  a  collar  bone 

r,  a  rib  d,  the  diaphragm 

Notice  the  effect  of  a  change  in  position  of  the 
diaphragm. 


46  THE  AIR  AND  HOW  WE  USE  IT 

enlarged.  The  elastic  lungs  which  are  in  direct  communication 
with  the  outside  air  therefore  become  bigger,  because  of  the  air 
pressure  of  fifteen  pounds  to  the  square  inch  which  forces  them 
against  the  diaphragm  and  sides  of  the  chest.  (See  diagram.) 
Then  when  the  diaphragm  goes  back  into  its  former  position, 
the  air  is  forced  out.  This  motion  of  the  diaphragm  is  kept  up 
throughout  our  lives  every  time  we  breathe. 

The  value  of  deep  breathing.  It  is  well  to  take  breathing  exer- 
cises every  day,  for  they  help  to  enlarge  the  lung  capacity.  Per- 
haps the  best  times  to  do  this  are  directly  after  arising  and  just 
before  retiring.  A  good  exercise  is  to  raise  the  arms  slowly  from 
the  sides  and  at  the  same  time  take  a  deep  breath.  Hold  the 
breath  two  or  three  seconds  am}  then  exhale.  The  whole  exer- 
cise should  take  about  ten  seconds.  Repeat  about  six  or  eight 
times. 

Oxidation  in  the  cells  of  the  body.  We  have  learned  how  air 
goes  in  and  out  of  the  lungs.  The  most  important  part  of  the 
breathing  process  does  not  take  place  in  the  lungs  but  in  the  body- 
cells.  We  know  that  oxygen  is  breathed  into  the  lungs,  and  there 
is  picked  up  by  the  red  corpuscles  and  taken  around  the  body  to  be 
given  off  to  the  cells.  Now  we  want  to  find  out  what  its  use  is  in  the 
cells.  Every  cell  contains  living  matter,  which  we  call  protoplasm, 
Chemists  have  found  that  protoplasm  is  a  very  complicated  sub- 
stance, made  of  several  different  elements.  The  most  important 
elements  are  carbon,  oxygen,  hydrogen,  and  nitrogen.  When  the 
oxygen  comes  in  contact  with  protoplasm,  oxidation  takes  place. 
The  carbon  and  the  oxygen  unite  to  form  carbon  dioxide;  the 
hydrogen  and  the  oxygen  form  water;  and  the  nitrogen  unites 
with  oxygen  and  several  other  elements  to  form  poisonous  waste 
materials. 

Whenever  oxygen  unites  with  other  elements  a  certain  amount 
of  heat  is  produced.  When  the  oxidation  goes  on  in  the  living 
cells,  the  heat  is  given  off  there.  That  is  what  keeps  the  body 
warm,  and  gives  it  the  energy  to  do  its  work. 

What  becomes  of  the  waste  matter.  It  would  be  very  harm- 
ful to  a  living  body  to  keep  its  waste  matter  stored  up  inside  the 
cells  or  even  near  the  cells.  So  every  living  creature  has  a  way  of 


AIR  AND  BREATHING  47 

getting  rid  of  its  waste.  Plants  send  out  the  carbon  dioxide,  the 
water,  and  the  poison  through  the  cell  walls  into  the  air  spaces  and 
finally  out  of  the  breathing  pores  in  the  leaves.  Animals  all  have 
some  breathing  system  which  carries  off  the  waste.  A  fish  has  gills, 
for  example.  In  human  bodies  the  three  wastes  are  gotten  rid 
of  as  follows:  (i)  Carbon  dioxide  passes  through  the  cell  walls  into 
the  liquid  part,  or  plasma,  of  the  blood,  by  which  it  is  carried  to 
the  lungs.  There  it  goes  through  the  thin  walls  of  the  tiny  blood 
vessels,  called  capillaries,  into  the  air  sacs  of  the  lungs,  and  finally 
out  through  the  nose  and  mouth.  (2)  Water  in  the  form  of  liquid 
is  taken  into  the  blood  from  the  cells,  and  finally  passes  out  of 
the  body  principally  through  the  kidneys  and  through  the  skin 
as  perspiration.  Some  of  the  water  is  changed  to  vapor  and  is 
breathed  out  of  the  nose  and  mouth.  (3)  The  poisonous  wastes 
are  given  off  in  all  three  ways,  by  means  of  the  kidneys,  the  skin, 
and  the  breathing  system. 

Artificial  respiration.  When  a  person  is  apparently  drowned  or 
overcome  by  gas  there  are  certain  restorative  measures  that  should 
be  applied.  If  possible,  send  for  a  doctor;  but  if  the  case  is  a 
serious  one,  do  not  wait  until  the  doctor  comes  before  acting.  In 
all  cases  there  are  certain  general  things  to  be  done,  (i)  See  that 
nothing  interferes  with  the  access  of  air  to  and  from  the  person's 
lungs.  (2)  Force  air  into  and  out  of  the  lungs.  This  process  is 
known  as  artificial  respiration. 

Let  us  suppose  that  a  person  has  been  brought  out  of  the  water 
unconscious  and  that  breathing  has  almost  or  entirely  ceased. 
The  first  thing  to  do  is  to  loosen  the  clothing  about  the  neck  and 
get  the  water  out  of  the  lungs.  This  can  be  done  by  raising  the 
body  at  the  middle  and  gently  shaking  it,  at  the  same  time  having 
the  tongue  pulled  out  so  as  to  have  free  access  from  the  lungs  to 
the  outside.  In  this  position  the  head  will  be  lower  than  the 
lungs  and  the  water  should  run  out  of  the  mouth.  The  tongue 
should  be  kept  extended  during  this  and  the  succeeding  opera- 
tions. The  next  step  is  to  put  the  person  into  a  horizontal  posi- 
tion and  apply  artificial  respiration. 

The  most  common  method  of  giving  artificial  respiration  is 
shown  in  the  illustration.  When  the  arms  are  extended  above  the 


48 


THE  AIR  AND  HOW  WE  USE  IT 


head  the  chest  cavity  is  enlarged  with  the  result  that  air  is  taken 
in.     The  air  is  forced  out  from  the  lungs  by  pressing  against  the 

sides  of  the  chest.  You 
can  time  the  process  by 
ybur  own  breathing.  The 
circulation  of  blood  and 
the  action  of  the  heart 
may  be  stimulated  by  ap- 
plying warm  cloths,  slap- 
ping the  arms  and  legs,  or 
applying  electricity.  The 
most  important  thing, 
however,  is  to  start  the 
breathing.  The  artificial 
respiration  should  be  con- 
tinued until  it  becomes 
evident  that  the  case  is 
either  hopeless  or  until  the 
person  breathes  of  him- 
self. Some  people  have 
been  saved  by  continuing 
the  artificial  respiration 
for  an  hour  or  even  longer 
when  apparently  no  hope 
of  recovery  existed. 

The  pulmotor  is  an  in- 
strument   by    means    of 


FIG.  34.  Artificial  respiration.  Kneeling  astride 
of  the  legs,  as  shown  in  the  picture,  place  both 
hands  on  the  small  of  the  back  and  throw  your 
weight  forward,  so  as  to  press  out  the  air  in  the 
lungs.  Count  three,  then  swing  backward,  lifting 
the  hands,  and  allow  the  lungs  to  fill  themselves 
with  air  for  three  seconds,  then  again  plunge  for- 
ward and  force  the  air  out  of  the  lungs  and  again 
lift  your  weight  and  allow  the  air  to  flow  in  for 
three  seconds.  Keep  up  this  swinging  backward 


and  forward  about  ten  or  twelve  times  a  minute. 

strument  by  means 
which  artificial  respiration  is  produced.  If  one  can  be  obtained 
and  its  operation  is  understood,  it  is  a  more  efficient  means  of 
rendering  assistance  than  the  methods  explained. 

INDIVIDUAL  PROJECTS 

Working  projects: 

1.  Examine  and  make  drawings  of  different  kinds  of  cells  as  seen  with  the 
compound  microscope.     The  teacher  may  furnish  prepared  slides  and 
give  a  brief  explanation  of  how  they  were  made. 

2.  Make  diagrams  to  show  the  air-passages  and  lungs  of  the  human  body. 

Essentials  of  Biology.     G.  W.  Hunter.     American  Book  Co. 
Primer  of  Sanitation.     J.  W.  Ritchie.     World  Book  Co. 

3.  Demonstrate  how  a  pulmotor  works. 


AIR  AND  BREATHING  49 

Reports: 

1.  How  different  animals  breathe;  i.e.,  fishes,  frogs,  insects,  and  birds. 
Several  pupils  may  work  on  this  project. 

Applied  Biology.     M.  A.  Bigelow.     American  Book  Co. 
Essentials  of  Biology.     G.  W.  Hunter.     American  Book  Co. 

2.  The  uses  of  gases  and  gas  masks  in  war. 

Scientific  American  Supplement,  March  2,  1918. 

3.  Animals  that  hibernate. 

BOOKS  THAT  WILL  HELP  YOU 

First  Aid  for  Boys.     Cole  and  Ernst.     D.  Appleton  &  Co. 

Good  Health.     F.  G.  Jewett.     Ginn  &  Co. 

Handbook  of  Health.     Woods  Hutchinson.     Houghton  Mifflin  Co. 

The  Human  Mechanism.     Hough  and  Sedgwick.     Ginn  &  Co. 

"Pumping  Air  into  the  Lungs  to  save  Human  Life."     Scientific  American 

Supplement,  April  8,  1916. 
"Supplying  Fresh  Air  through   Canvas  Tubes  to  Underground  Workers." 

Scientific  American  Supplement,  June  24,  1916. 


PROJECT  IV 
AIR  AND  HEALTH 

Fresh  air.  These  are  the  days  when  we  hear  much  about  the 
out-of-doors.  Many  go  camping,  and  every  one  seems  to  realize 
that  fresh  air  is  a  vital  necessity.  People  who  can  afford  to  do 

so  very  often  build  sleep- 
ing-porches. The  old  idea 
that  night  air  is  harmful  has 
been  shown  to  be  untrue 
In  fact,  night  air  in  cities 
is  apt  to  be  purer  than  day 
air  because  there  is  rela- 
tively little  traffic  at  night, 
and  hence  less  dust.  Every- 
one who  can  possibly  ar- 
range to  do  so  should  spend 
at  least  two  hours  a  day 
out-of-doors.  If  this  were 
done,  there  would  be  fewer 
colds,  sore  throats,  and 
other  diseases  of  the  respi- 
ratory system.  It  is  a  well- 
known  fact  that  men  who 
spend  much  time  in  the 
"  open  "  very  seldom  suffer 
from  such  diseases. 

Much  of  our  time  must 
be  spent  indoors,  however. 
To  find  out  the  best  ways  of  ventilating  the  rooms  where  we 
must  be,  try  problems  I  and  2.  The  other  problems  in  this 
project  all  deal  with  our  invisible  enemies,  the  disease-producing 
bacteria.  If  you  wish  to  find  out  still  more  about  them,  start 
some  of  the  individual  projects  suggested  on  page  66. 


FIG.  35.  An  open-air  school. 


AIR  AND  HEALTH  51 

PROBLEMS 

PROBLEM  i :  WHAT  is  THE  BEST  WAY  TO  VENTILATE  A  LIVING-ROOM? 
Directions: 

(Note  —  Of  course,  living-rooms  can  usually  be  ventilated  by  having 

draughts  from  halls  or  other  rooms  sweep  through.     In  this  problem, 

however,  we  shall  not  consider  this  method,  but  rather  how  to  ventilate 

a  room  shut  off  by  itself.) 

The  test  should  be  made  on  a  quiet  day.  Light  some  joss  sticks  and 
hold  them  at  open  windows.  Try  the  experiment  when  the  windows  are 
open  at  the  bottom  and  at  the  top.  Try  as  many  different  combinations 
as  possible.  Try,  by  means  of  the  smoke  of  the  burning  joss  sticks,  to  fol- 
low the  air  currents.  Determine  which  combination  results  in  producing 
the  desired  effect;  that  is,  in  giving  cool  fresh  air  to  all  parts  of  the  room 
without  draughts. 

Summary: 

Write  a  report  upon  your  experiment,  using  diagrams. 

PROBLEM  2:  WHAT  is  THE  BEST  WAY  TO  VENTILATE  THE  SCHOOLROOM? 

Directions: 

Part  i :  If  a  special  ventilating  system  has  been  installed  in  your  school, 
perform  the  following  experiment: 

Close  all  windows,  doors  and  transoms.  Put  joss  sticks  at  the  ventilation 
openings  in  ordet  to  determine  which  is  the  one  carrying  air  into  the  room 
and  which  is  for  the  purpose  of  carrying  the  used  air  out.  By  holding  burn- 
ing joss  sticks  at  different  places  in  the  room  try  to  determine  the  course 
taken  by  the  air. 

Do  you  find  air  motion  in  all  parts  of  the  room?  Find  out  the  source  of 
the  entering  air  and  what  is  done  to  it  before  it  is  admitted  to  the  school- 
room. Also  find  out  where  the  used  air  goes  after  it  leaves  the  room. 

Part  2 :  If  there  is  no  special  ventilating  system  in  your  school  perform 
experiments  similar  to  those  outlined  under  problem  i. 

Summary: 

1.  Write  a  report  of  your  experiment. 

2.  What  method  gives  the  best  results? 

PROBLEM  3:  DOES  THE  AIR  CONTAIN  BACTERIA? 

Directions: 

Expose  for  five  minutes  some  Petri  dishes  containing  nutrient  agar  to  the 
air  of  the 

(1)  Schoolroom. 

(2)  Hall  during  the  passing  of  classes. 

(3)  Out-of-doors. 


52  THE  AIR  AND  HOW  WE  USE  IT 

Put  these  dishes  away  in  some  place  where  they  will  be  kept  at  a  moder- 
ate temperature;  that  is,  from  60°  to  70°  Fahrenheit.  Compare  them  with 
other  dishes  which  were  not  exposed.  Examine  them  every  day  for  about 
a  week.  After  a  few  days,  if  the  material  was  properly  prepared,  different- 
colored  little  patches  or  dots  will  appear  in  the  dishes  that  were  exposed. 
Each  of  these  consists  of  millions  of  bacteria.  Each  one  is  called  a  col- 
ony, and  each  colony  came  from  a  single  bacterium  that  happened  to  fall 
upon  the  nutrient  agar.  Examine  some  of  the  material  from  the  colony 
under  the  microscope,  as  directed  in  the  next  problem. 

Summary: 

1.  Compare  the  number  of  bacteria  which  fell  into  the  dishes  in  each 
case. 

2.  Which  air  is  purest,  as  shown  by  this  one  experiment? 

PROBLEM  4:  To  SEE  BACTERIA  WITH  THE  MICROSCOPE. 

Directions: 

Place  a  drop  of  broth,  in  which  bacteria  have  been  growing,  upon  a  slide. 
Put  a  cover-glass  on  it  and  examine  with  the  high  power  of  the  microscope. 

Can  you  see,  when  the  light 
is  not  too  strong,  very  tiny 
shadow-like  forms?  They  are 
the  bacteria.  Some  or  all  of 
them  may  appear  to  be  mov- 
ing about  quite  rapidly.  What 
form  or  forms  do  they  possess? 
Place  a  small  drop  of  this 
material  upon  a  slide  and  let 

FIG.  36.  Bacteria  seen  through  a  microscope.  *  dlT-  When  ^  Put  some 
The  dish  at  the  left  contains  bacteria  which  produce  "methylene  blue"  upon  it. 
typhoid  fever;  those  at  the  right  cause  tuberculosis.  Let  it  stand  for  two  minutes 

and  then  wash  it  off  by  let- 
ting water  run  over  the  slide.  This  washing  will  not  remove  the  bacteria. 
The  slide  may  then  be  blotted  gently  and  the  stained  bacteria  examined 
with  the  microscope. 

Can  you  now  see  the  forms  more  distinctly? 

Drawing: 

Draw  in  your  notebook  the  forms  which  you  could  see. 

PROBLEM  5:  WILL  SUNLIGHT  KILL  BACTERIA? 

Directions: 

Expose  two  or  three  dishes  containing  nutrient  agar  in  a  dusty  place 
for  ten  or  fifteen  minutes.  Paste  some  heavy  paper  over  the  lids  with  holes 


AIR  AND  HEALTH  53 

in  the  center  about  one  inch  in  diameter.     Place  these  dishes  in  the  sun- 
light and  examine  the  contents  every  day  for  a  week.     What  is  the  result? 

Summary; 
Write  a  report  of  the  experiment  and  make  applications  to  home-life. 

PROBLEM  6:  How  MAY  BACTERIA  BE  DESTROYED? 

Directions: 

Arrange  a  series  of  six  or  more  test-tubes  containing  beef  broth.  Expose 
all  but  one  to  the  air  for  a  few  minutes  until  it  is  certain  that  bacteria  have 
entered.  (Another  method  of  doing  this  is  to  put  a  few  drops  of  tap  water 
into  each  tube.)  Label  the  tubes  as  follows  after  treating  the  tubes  as 
indicated  in  each  case: 

(1)  Not  exposed. 

(2)  Exposed. 

(3)  Exposed  plus  salt. 

(4)  Exposed  plus  hydrogen  peroxide. 

(5)  Exposed  plus  mercuric  chloride. 

(6)  Exposed  plus  carbolic  acid. 

(7)  Exposed  plus  other  disinfectant. 

Compare  the  appearance  of  these  tubes  every  day  for  a  week.  Often 
bacteria  growth  is  indicated  by  a  cloudy  appearance. 

After  a  week  examine  a  drop  from  each  tube  under  the  microscope  for 
bacteria. 

If  bacteria  are  present  in  the  broth  containing  the  antiseptics  or  disin- 
fectants, how  do  you  explain  the  fact?  If  this  is  the  case  it  might  be  ad- 
visable to  try  the  experiment  again  using  larger  amounts  of  these  sub- 
stances. 

Questions: 

1.  How  could  you  perform  an  experiment  to  find  out  whether  freezing 
kills  bacteria? 

2.  Why  are  hardwood  floors  to  be  preferred  to  carpeted  floors? 

PROBLEM  7 :  To  SHOW  HOW  THE  PREVALENCE  OF  SOME  DISEASES  DEPENDS 
UPON  SEASONAL  CHANGES. 

Directions: 

Procure  from  your  state  department  of  health,  and  if  you  live  in  a  large 
city,  from  your  city  board  of  health  as  well,  statements  regarding  the  num- 
ber of  deaths  each  month  of  the  preceding  year  from  the  following  causes: 
consumption,  pneumonia,  and  diphtheria. 

Make  three  charts  which  will  indicate  the  relative  number  of  deaths  each 
month  from  these  causes.  (For  the  form  of  these  charts,  see  page  64.) 
If  you  can  secure  the  average  number  of  deaths  from  these  causes  during 


54  THE  AIR  AND  HOW  WE  USE  IT 

the  past  ten  years  or  more,  compare  the  records  of  last  year  with  the  pre- 
ceding years.     Can  you  explain  the  reason  for  any  great  difference? 

Summary: 

What  conclusions  are  you  justified  in  making  regarding  the  effect  of  the 
seasons  upon  the  prevalence  of  consumption?  pneumonia?  diphtheria? 

Question: 

What  practical  use  can  be  made  of  the  information  obtained  and  shown 
in  the  charts? 

Factors  which  control  ventilation.  Have  you  ever  gone  to  the 
top  of  a  high  hill  on  a  fine,  breezy  day?  How  exhilarating  the  air 
felt!  How  different  you  feel  in  a  close  room  filled  with  people! 
The  air  in  these  two  places  is  different  in  many  respects,  in  its 
composition,  its  temperature,  and  especially  its  rate  of  motion. 

I.  Temperature  of  ah*.     The  air  on  the  hill  was  probably  con- 
siderably cooler  than  the  air  in  the  crowded  room.  There  is  always 
an  envelope  of  heated  air  that  surrounds  the  body.   The  temper- 
ature of  the  air  space  between  the  body  and  the  clothes  varies 
from  90  to  95  degrees,  Fahrenheit,  and  is  kept  at  this  temperature 
by  the  heat  from  the  body.    The  surrounding  air  is  usually  cooler 
than  this,  and  consequently  when  a  breeze  drives  the  heated  air 
away,  cooler  air  comes  in  to  take  its  place.     In  the  summer  time 
this  brings  a  feeling  of  relief;  hence,  the  use  of  electric  fans.     On 
the  other  hand,  in  the  winter  we  wear  heavy  clothing  to  keep  the 
heat  close  to  the  body. 

The  desirable  and  pleasing  effects  produced  by  sleeping  in  a 
room  with  the  windows  open  are  due  mainly  to  the  fact  that  the 
air  is  usually  kept  cool  and  in  motion.  Stagnant  air  is  depressing; 
moving  air  is  apt  to  be  exhilarating. 

Have  you  ever  heard  of  the  Black  Hole  of  Calcutta,  where  146 
English  prisoners  were  left  overnight  in  a  guardroom  18  feet  by  14 
feet  with  but  two  small  windows?  In  the  morning  only  23  were 
left  alive.  It  used  to  be  thought  that  such  a  death  was  due  to  the 
large  accumulation  of  carbon  dioxide.  It  is  now  known  that  the 
deaths  were  due  to  a  much  greater  extent  to  an  interference  of  the 
bodily  functions  caused  by  the  excessive  heat,  the  stagnation  of 
the  air,  and  the  great  amount  of  water  vapor  that  was  present. 

II.  Amount  of  water  vapor  in  the  air.    The  air  is  never  abso- 


AIR  AND  HEALTH  55 

lutely  dry.  There  is  always  moisture  in  it  in  the  form  of  an  in- 
visible gas,  called  water  vapor.  The  amount  of  water  vapor  present 
in  the  air  exerts  a  very  marked  effect  upon  our  comfort  and  well- 
being.  We  all  know  that  some'days  are  spoken  of  as  being  "  close." 
In  the  summer,  especially,  days  of  this  kind  are  very  disagreeable. 
At  such  times  the  amount  of  water  in  the  air  is  very  great.  On 
other  days  when  the  air  is  drier  we  generally  feel  more  active. 

From  these  facts  it  might  be  taken  for  granted  that  it  would  be 
well  to  have  our  rooms  so  ventilated  as  to  take  away  as  much  of  the 
moisture  from  the  air  as  possible.  This,  however,  would  not  be  a 
correct  conclusion.  A  moderate  amount  of  moisture  in  the  air 
is  necessary  for  health. 

HI.  Foreign  materials  in  the  air.  The  most  common  kind  of 
foreign  material  in  the  air  is  dust.  When  much  of  this  is  present, 
it  is  capable  of  doing  serious  harm,  (i)  It  may  irritate  the  delicate 
lining  of  the  air  passages  and  lungs.  (2)  It  is  the  means  of  carry- 
ing bacteria  into  the  body,  some  of  which  may  cause  disease. 
Some  ventilating  systems  have  an  arrangement  for  giving  the  air 
brought  in  from  outside  a  shower-bath.  It  is  usually  impossible 
to  install  a  ventilating  system  of  this  kind  in  our  homes,  but  it  is 
possible  even  here  to  keep  dust  down  to  a  minimum  by  proper 
methods  of  dusting  and  cleaning.  A  city  government  can  do  much 
in  the  way  of  preventing  dust  by  flushing  the  streets  and  enforcing 
laws  that  require  factories  to  be  provided  with  arrangements  for 
keeping  the  air  clean.  Certain  industries  are  extremely  danger- 
ous to  the  health  of  the  workers  because  of  the  fact  that  different 
kinds  of  dust  particles  are  produced  and  get  into  the  air  that  is 
breathed  by  the  workers.  Metallic  dust  and  dust  from  felt  in  facto- 
ries where  hats  are  made  are  common  examples  of  dust  which  is 
harmful  to  workers.  In  many,  if  not  all  cases,  remedies  might  be 
adopted  to  protect  them,  and  it  should  be  the  business  of  the  city 
or  -state  to  see  that  this  is  done. 

Cleaning  and  dusting.  The  best  kind  of  cleaning  apparatus  for  use  in 
the  home  is  the  vacuum  cleaner.  This  mechanism  sucks  the  dust  into 
a  bag  from  which  it  may  be  emptied  and  destroyed.  The  worst  thing 
that  can  be  used  is  the  feather  duster.  This  method  of  cleaning  merely 
stirs  the  dust  so  that  it  floats  in  the  air,  from  which  it  may  be  inhaled 


56  THE  AIR  AND  HOW  WE  USE  IT 

or  fall  back  again  upon  the  surfaces  of  the  very  things  that  a  short  time 
before  were  dusted.  A  cloth  or  mop  dampened  with  water  or  oil  is  serv- 
iceable for  certain  kinds  of  cleaning  and  does  not  have  the  objectionable 
feature  of  a  feather  duster  or  dry  cloth.  Heavy  curtains,  carpets,  and  rugs 
are  dust-collectors  and  if  used  should  be  thoroughly  cleaned  at  regular 
intervals. 

Air  and  disease.  We  sometimes  hear  it  said  that  a  "  change  of 
air"  is  a  good  thing  for  people  suffering  from  or  threatened  by 
certain  diseases.  Thus,  consumptives  are  often  sent  away  to  a 
"dry  climate"  with  the  result  that  sometimes  their  lives  are 
saved.  Again,  it  is  quite  generally  known  that  certain  diseases  are 
what  are  called  "air  borne "  diseases.  This  means  that  the  living 
organisms  which  must  enter  the  body  to  cause  the  diseases  are 
carried  through  the  air.  The  little  living  organism  which  causes 
consumption  is  sometimes  found  in  dust.  Because  certain  dis- 
eases are  communicable,  it  is  necessary  to  isolate  or  quarantine 
the  persons  suffering  from  them.  Before  the  quarantine  may  be 
broken,  the  room  or  premises  occupied  by  the  patient  should  be 
cleansed  or  freed  as  far  as  possible  from  the  organisms  causing  the 
disease.  The  process  of  freeing  from  living  organisms  is  called 
disinfection.  It  is  worth  while  to  know  something  about  the  sig- 
nificance or  meaning  of  these  facts  so  that  we  may  know  how  to 
act  as  individuals  and  how  our  communities  should  act  to  safe- 
guard our  own  lives  and  health,  as  well  as  those  of  the  people 
about  us. 

Enemies  of  health.  Except  in  the  case  of  certain  diseases,  such 
as  cancer,  which  still  baffle  the  researches  of  scientists,  it  has  been 
determined  that  diseases  are  produced  by  the  entrance  into  the 
body  of  little  living  organisms  which  are  commonly  called  germs. 
The  term  germ,  however,  is  not  only  applied  to  all  kinds  of  dis- 
ease-producing organisms  but  to  certain  other  things  as  well. 
For  this  reason  we  should  avoid  its  use.  The  most  common  kinds 
of  disease-producing  organisms  are  bacteria,  which  are  the  simplest 
kind  of  plants. 

Bacteria  are  so  very  small  that  several  millions,  even  of  the 
larger  varieties,  may  be  contained  in  an  ordinary  drop  of  liquid. 
They  are  classified  in  three  groups  according  to  their  form  or 


AIR  AND  HEALTH 


57 


shape.  A  study  of  the  illustration  will  show  how  they  look  when 
viewed  under  the  microscope.  Not  all  bacteria  are  capable  of  pro- 
ducing disease.  Many,  in  fact,  are  very  useful;  some  are  abso- 
lutely necessary  for  life.  (Seepage  88.)  The  kinds  which  cause 
disease  are  few  and  are  exceptional  varieties,  but  because  they  do 
so  much  harm  they  are  the 
best  known  and  most  talked 
about. 

How  bacteria  enter  the 
body.  Bacteria  usually  enter 
the  body  through  the  nose  or 
mouth.  They  may  get  in  with 
air  that  is  breathed.  They 
enter  with  the  food.  They  are 
often  brought  to  the  mouth 
and  nose  through  the  medium 
of  the  hands.  This  fact  should 
result  in  making  us  think 
about  the  importance  of  clean- 

liness    in  Our  daily  living  and 

especially  of  the  importance 

of   often   Washing   hands    and 

face.  It  is  interesting  to  know, 

however,   in    this   connection 

that  very  few  bacteria  can  enter  the  body  through  the  unbroken 

skin.     Some  of  them,  however,  can  quite  readily  grow  upon  the 

more  delicate  lining  of  the  air  passages  and  thus  may  cause  colds 

and  sometimes  more  serious  diseases  such  as  bronchitis,  la  grippe, 

influenza,  pneumonia,  and  consumption. 

How  bacteria  attack  the  body.  Usually  the  bacteria  that  are 
capable  of  producing  the  diseases  that  have  just  been  mentioned 
do  not  cause  trouble  unless  the  body  has  been  weakened  in  some 
manner.  In  other  words,  they  find  it  difficult  to  harm  a  person 
who  is  in  good  physical  condition.  They  all  have  the  power  of 
making  poisons,  which  weaken  the  body  and  cause  disease.  The 
tubercle  bacillus,  the  bacterium  causing  tuberculosis,  is  different 
from  others  in  that  it  actually  destroys  considerable  amounts  of 


FIG.  37.  Bacteria. 

Row  A,  five  different  kinds  of  rod-shaped 


Row  B,    coccus  forms  —  single,   chained, 

forms.    D>  branched  forms< 


58  THE  AIR  AND  HOW  WE  tfSE  IT 

body  tissues.  Thus,  the  person  who  dies  from  consumption  will 
have  parts  of  one  or  both  lungs  entirely  eaten  away  or  consumed. 
Hence  the  name  "  consumption." 

How  bacteria  increase  in  number.  It  may  at  first  thought  seem 
strange  that  such  very  small  things  as^  bacteria  can  produce 
enough  poison  to  make  a  person  seriously  ill.  There  are  two  ex- 
planations of  their  injurious  effect  upon  the  body,  (i)  Bacteria 
multiply  or  reproduce  very  rapidly.  From  a  very  few,  countless 
millions  may  be  produced  in  two  or  three  days.  (2)  Some  of  the 
poisons  which  they  make  are  so  extremely  powerful  that  only  a 
little  is  needed  to  cause  serious  trouble. 

Bacteria  reproduce  in  a  very  simple  manner.  One  of  them  di- 
vides into  two  parts,  and  each  half  under  favorable  conditions 
becomes  as  large  as  the  bacterium  from  which  it  came.  Then  each 
half  likewise  divides  and  produces  two  more.  This  process  will 
be  kept  up  indefinitely  as  long  as  favorable  conditions  last.  For- 
tunately, favorable  conditions  do  not  usually  last  a  very  long  time. 
If  they  did,  this  world  in  a  short  time  would  be  covered  by 
nothing  but  bacteria.  Sometimes  the  bacteria  stop  multiplying 
because  they  are  killed  by  their  own  poisons  or  because  their 
food-supply  gives  out. 

In  order  to  realize  how  rapidly  bacteria  reproduce,  consider  how  many 
may  come  from  a  single  bacterium  in  twenty-four  hours,  if  it  belongs  to  a 
group  that  can  reproduce  every  hour.  Many  can  produce  even  more 
rapidly  than  this.  Starting  with  one,  at  the  end  of  one  hour  there  will  be 
two.  At  the  end  of  two  hours,  four.  Then  the  numbers  will  jump  to 
eight,  sixteen,  thirty-two,  sixty-four,  one  hundred  twenty -eight,  etc., 
until  at  the  end  of  twenty-four  hours  we  find  that  they  reach  the  stupen- 
dous sum  of  20,082,968.  This  figure  is  not  an  exaggeration,  as  any  one 
may  determine  for  himself. 

How  the  body  defends  itself  against  the  attacks  of  bacteria. 
If  bacteria  are  around  us  in  such  huge  numbers  and  the  body 
presents  such  easy  ways  of  entrance,  why  does  it  not  at  once  suc- 
cumb to  their  attacks?  There  are  several  means  of  defense  with 
which  nature  has  supplied  us  in  our  fight  against  bacteria.  These 
defenses  may  be  divided  into  two  groups,  the  external  and  the  in- 
ternal. Let  us  consider  first  the  external  defenses. 


AIR  AND  HEALTH  59 

The  external  defenses,  i.  Much  of  the  dust  that  would  other- 
wise get  into  the  wind-pipe,  is  caught  by  the  hairs  of  the  nose. 
Hence  we  can  see  one  reason  of  great  importance  for  always 
breathing  through  the  nose. 

2.  The  dust  which  is  carried  past  the  hairs  of  the  nose  meets 
with  a  serious  obstacle  to  its  passage  into  the  lungs,  in  the  form 
of  certain  tiny  structures  which  are  found  in  the  wind-pipe.  These 
minute  structures,  which  are  microscopic  threads  of  living  matter, 
are  known  as  cilia.     The  cilia  have  the  power  of  motion,  and  lash 
more  rapidly  in  an  upward  direction  than  in  a  downward  direc- 
tion.    This  movement  causes  any  dust  which  may  settle  on  the 
inside  of  the  wind-pipe  to  be  raised  or  coughed  up.     If  it  were  not 
for  the  action  of  these  cilia,  it  would  not  be  very  long  before  the 
lungs  would  be  clogged  with  dust  and  breathing  would  become 
difficult.    (See  figure  31  on  page  44.) 

3.  The  mouth  also  contains  a  means  of  defense  against  the 
harmful  action  of  bacteria.     This  is  found  in  the  digestive  juice 
or  saliva  which  is  poured  into  it.     Saliva  does  not  kill  the  bacteria 
which  may  enter  the  mouth,  but  it  does  not  offer  a  good  medium 
for  their  growth  and  multiplication.     It  usually  prevents  their  re- 
production and  weakens  them. 

4.  The  nose,  mouth,  and  tubes  leading  to  the  lungs  all  have 
the  same   kind  of  lining  which  is  called   the  mucous  membrane. 
This  membrane  usually  offers  another  means  of  defense  against 
the  action  of  bacteria.     When  in  a  healthy  state  it  is  not  a  favor- 
able place  for  the  growth  of  bacteria.      However,  if  this  mem- 
brane becomes  inflamed  or  irritated,  conditions  are  quite  changed. 
Bacteria  find  it  a  favorable  breeding-place  and  may  then  cause 
trouble.      In  this  way  colds,  pneumonia,  and  consumption  may 
originate. 

Internal  defenses.  Besides  these  external  means  of  defense, 
the  body  is  supplied  with  internal  defenses,  so  that  when  bacteria 
find  lodgment  in  the  body  and  proceed  to  cause  a  disease,  they 
themselves  are  usually  attacked  and  frequently  killed.  The  body 
has  two  great  means  of  thus  defending  itself,  (i)  There  are 
millions  of  cells  in  the  blood  called  white  corpuscles,  that  have 
the  power  of  attacking  and  eating  certain  forms  of  bacteria. 


6o 


THE  AIR  AND  HOW  WE  USE  IT 


(2)  There  are  certain  body  fluids  that  are  frequently  able  to  kill 
bacteria. 

I.  The  white  cells  of  the  blood.  The  white  corpuscles  are  often 
called  the  standing  army  of  the  body.  In  many  cases,  especially 
where  bacteria  attack  the  body  through  cuts  and  wounds  these 
white  corpuscles,  of  which  there  are  usually  seven  thousand  in 
every  drop  of  blood,  are  attracted  to  the  spot 
and  proceed  to  attempt  to  destroy  the  bac- 
teria by  engulfing  them.  They  use  the  bac- 
teria as  food,  providing  they  are  in  sufficient 
strength  and  numbers  and  providing  the  bac- 
teria are  not  too  powerful.  Sometimes  the 
bacteria  gain  the  upper  hand  and  by  their 
poisons  kill  off  the  white  corpuscles. 

A  drop  of  pus  or  the  sputum  of  a  consump- 
tive when  viewed  under  the  microscope  will 
show  that  a  pitched  battle  has  been  fought. 
Some  of  the  body  cells  can  be  seen  to  have 
been  killed  by  the  bacteria  and  on  the  other 
hand  some  bacteria  can  be  seen  to  have  been 
overcome  by  the  cells. 

2.  Some  body  fluids  act  as  a  defense.  In 
addition  to  the  white  corpuscles  the  blood 
has  other  means  of  destroying  certain  bac- 
teria and  their  poisons.  In  the  case  of  diph- 
theria, the  bacteria  which  live  in  the  throat  give  off  a  powerful 
poison,  or  toxin,  that  enters  the  blood  and  causes  the  fever. 
When  a  person  recovers  from  this  disease  it  is  because  his  body 
was  able  to  make  enough  of  a  certain  kind  of  fluid  to  destroy 
this  poison. 

Antitoxin  treatment  is  an  example  of  this  method  of  fighting 
the  disease.  Antitoxin  is  usually  obtained  from  a  horse.  The 
most  common  disease  for  which  it  is  used  is  diphtheria. 

The  antitoxin  treatment  for  diphtheria.  Diphtheria  bacilli  are  grown  in 
a  meat  broth.  They  give  off  their  poisons  which  are  then  taken  and  care- 
fully measured.  A  certain  amount  of  this  poison,  called  toxin,  is  then  in- 
jected; that  is,  put  into  the  horse's  blood.  Not  enough  is  put  in  seriously 


FIG.  38.  A  contest  be- 
tween a  white  corpuscle 
and  a  bacterium.  The 
corpuscle  is  shown  ap- 
proaching, touching,  en- 
gulfing, and  beginning 
to  digest  the  bacterium. 


AIR  AND  HEALTH 

to  injure  the  animal.  After  a  few  days  a  larger  dose  is  injected.  This  is 
repeated  at  regular  intervals  until  the  horse  can  stand  an  amount  of  this 
poison,  which,  if  injected  at  first,  would  have  killed  him.  Then,  however, 
the  animal  has  become  accustomed  to  the  poison,  and  shows  no  harmful 
effect  whatever  from  the  dose.  The  reason  for  this  is  that  the  horse's  blood 
has  been  making  what  is  called  antitoxin,  which  has  the  power  of  neutraliz- 
ing or  destroying  the  toxin.  The  animal  is  then  bled.  The  blood  is 
treated  in  such  a  way  as  to  obtain  the  antitoxin.  This  antitoxin  is  meas- 
ured and  certain  quantities  are  distributed  for  use  by  doctors.  Thus  when 
a  doctor  injects  antitoxin  into  a  person  who  has  either  developed  diphtheria 
or  has  been  exposed  to  it,  he  is  putting  into  that  person's  body  just  the 
weapons  that  are  needed  to  fight  against  the  poisons  made  by  the  diph- 
theria bacillus. 

Bacteria  present  in  healthy  people.  It  has  been  found  in  recent 
years  that  some  forms  of  disease-producing  bacteria  are  usually 
present  in  the  mouths  of  well  people.  Thus,  many  healthy  people 
may  carry  around  with  them  the  agents  that  cause  such  serious 
diseases  as  tuberculosis,  pneumonia,  and  diphtheria.  Practically 
every  one  of  us  has  in  his  mouth  at  one  time  or  another  the  bac- 
teria which  cause  colds  even  when  we  are  entirely  free  from  cold. 
These  bacteria  simply  need  a  weakening  of  the  defenses  of  the 
body  in  order  to  give  them  the  proper  conditions  to  grow  and 
cause  sickness. 

Importance  of  keeping  the  body  in  a  healthy  condition.  There 
is  excellent  reason  for  believing  that  most  people  who  have 
reached  the  age  of  thirty  have  been  attacked  by  the  tubercle 
bacilli.  However,  because  of  their  bodily  power  of  resistance 
they  have  been  able  to  overcome  the  bacteria. 

Although  consumption  cannot  exist  unless  the  tubercle  bacillus 
is  present  in  the  lungs,  nevertheless  the  mere  presence  of  the  bac- 
teria does  not  always  cause  people  to  become  ill  with  the  disease. 
Neither  is  the  disease  inherited;  that  is,  passed  on  from  parent 
to  child.  Although  consumption  is  not  inherited,  it  is  true  that 
one  may  inherit  a  tendency  to  it.  In  other  words,  a  person  may 
inherit  weak  lungs  from  his  parents  and  a  lower  power  of  resist- 
ance to  the  disease  than  most  people  have.  The  most  impor- 
tant thing  to  do  in  avoiding  this  disease  is  to  keep  the  human  body 
in  such  vigorous  condition  that  the  bacteria  will  not  have  a 


THE  AIR  AND  HOW  WE  USE  IT 

,e  to  grow,  even  if  they  enter  the  body.  What  has  been 
in  regard  to  consumption  is  true  of  most  other  diseases  as 

;1.  A  body  that  is  weakened  by  any  cause  offers  a  lowered 
resistance  to  the  inroads  of  bacteria.  Within  certain  limits,  it  is 
possible  and  practicable  for  us  to  maintaifi  our  bodily  resistance 
to  the  degree  that  we  ourselves  desire. 

How  to  keep  well.  What  shall  we  do  to  keep  the  body  in  good 
condition?  Breathe  through  the  nose.  Eat  enough  clean,  whole- 
some food.  People  who  are  undernourished  are  more  apt  to  fall 
prey  to  disease  than  others.  Get  plenty  of  sleep.  Most  people 
need  at  least  eight  hours  sleep  every  night,  and  young  people 
usually  require  nine  or  ten.  Try  to  have  clean  surroundings. 
Get  out  of  doors  as  much  as  possible  and  have  your  living-room 
ventilated  properly.  Arrange  to  have  some  exercise  every  day, 
preferably  in  the  open  air.  As  to  the  things  not  to  do,  avoid 
drinking  alcoholic  beverages.  DC  not  smoke.  Avoid  excesses 
of  all  kinds. 

Effects  of  alcohol  and  tobacco.  Smoking  irritates  the  lining 
membrane  of  the  lungs  and  air  passages.  Alcohol  also  weakens 
the  organs  of  breathing  and  makes  them  susceptible  to  disease. 
Physicians  know  that  a  "drinker"  has  not  a  good  chance  of  re- 
covering from  pneumonia.  Although  smoking  and  "drinking" 
cannot  in  themselves  cause  consumption,  it  is  true  that  many 
have  died  from  this  disease  who  have  weakened  their  bodies  by 
such  habits. 

The  effect  of  alcohol  on  the  body  is  fourfold.  First  it  acts  as 
an  irritant,  then  a  stimulant,  then  a  depressant,  and  finally  para- 
lyzes the  nerve  centers.  The  effect  varies  with  the  individual  and 
the  bodily  condition.  In  a  " typhoid  condition"  more  alcohol 
can  be  absorbed  than  in  health.  In  certain  diseases  associated 
with  debility,  alcohol  is  very  valuable  as  a  medicine.  Any  idea 
that  the  drinking  of  alcohol  serves  to  protect  a  person  against 
disease  is  entirely  wrong,  however.  The  body  is  weakened  in 
time,  so  that  it  is  less  able  to  recover  from  the  effects  of  disease. 
Not  only  are  diseases  of  the  lungs  and  breathing  system  apt  to 
attack  the  drinking  man ;  but  many  other  diseases  find  him  sus- 
ceptible to  attack. 


AIR  AND  HEALTH  63 

Some  facts  collected  by  life  insurance  companies  as  to  the  rela- 
tion between  the  use  of  alcohol  and  length  of  life  follow : 

MEN  WHO  INDULGED  IN  OCCASIONAL  ALCOHOLIC  EXCESSES 

Ratio  of  actual  to 

expected  deaths. 

Expected  deaths 

represented  by  100% 

One  excess  or  more,  the  last  within  2  years  of  application  for 

insurance 174% 

One  excess  or  more,  2-5  years  before  application 148% 

One  excess  or  more,  5-10  years  before  application 150% 

One  excess  or  more,  more  than  10  years  before  application. . .  139% 

Among  those  said  to  use  alcohol  to  excess  occasionally  it  is  evi- 
dent that  the  mortality  is  distinctly  high.  The  death-rate  from 
suicide  and  accident  was  much  higher  than  normal,  also.1 

Dr.  W.  E.  Porter,  President  of  the  Association  of  Life  Insurance 
Medical  Directors  of  America,  draws  the  following  conclusion 
after  a  thorough  study  of  the  effects  of  the  use  of  alcohol  on  the 
length  of  life  of  over  15,000  clerks,  22,000  merchants,  13,000  sales- 
men, 27,000  farmers,  and  5000  factory  superintendents: 

"The  investigation  shows  that,  roughly,  the  average  mortality 
among  total  abstainers  from  alcohol  is  68.4%,  whereas  that  of  the 
non-abstainer  is  91.5%,  a  difference  of  23.1%.  This  means  a 
reduction  of  about  two  and  one  third  years  in  the  average  life  of 
the  non-abstainer,  below  that  of  the  abstainer." 

Seasons  in  relation  to  the  prevalence  of  disease.  It  is  com- 
monly known  that  at  certain  seasons  people  are  apt  to  have  cer- 
tain forms  of  disease.  The  winter  and  spring  are  the  seasons  when 
colds,  grip,  pneumonia,  diphtheria,  and  tuberculosis  are  most 
prevalent.  Knowing  this,  we  should  be  on  our  guard  especially 
at  these  seasons.  Colds,  coughs,  and  sore  throats  should  not  be 
neglected,  and  draughts  and  wet  feet  should  be  avoided  as  far  as 
possible.  It  will  be  profitable  for  you  to  make  tables  for  your  own 
state  similar  to  those  on  the  following  page,  which  as  you  see 
give  by  months  the  number  of  people  dying  from  diseases  of 
the  respiratory  system  for  the  year  1916  for  the  whole  country. 

Some  ways  in  which  bacteria  are  spread.  Tuberculosis  may  be  spread 
by  dried  sputum.  This  is  blown  about  by  the  wind,  the  bacteria  them- 

1  Courtesy,  New  England  Mutual  Life  Insurance  Company. 


64 


THE  AIR  AND  HOW  WE  ftSE  IT 


selves  not  being  able  to  fly.     While  disease  bacteria  may  be  transmitted 
to  persons  through  the  air,  the  most  common  means  of  transmission  from 


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FIG.  39.  Influence  of  season  on  disease.  Deaths  from  disease  by  months 
for  the  year  1916,  in  the  U.S.  Registration  Area,  which  represents  a  population 
of  about  72  million  people.  (Mortality  Statistics,  1916,  Bureau  of  the  Census.) 
Pneumonia,  scarlet  fever,  and  diphtheria  are  more  prevalent  in  cold  weather. 
Typhoid  and  diarrhoea  are  warm-weather  diseases.  Tuberculosis  is  less  affected 
by  the  seasons  than  the  others.  More  deaths  occur  from  it  in  cold  weather, 
but  the  difference  between  summer  and  winter  is  not  great. 

the  sick  to  the  well  is  by  direct  personal  contact.  Bacteria  causing  con- 
sumption, influenza,  pneumonia,  and  diphtheria  may  be  passed  from  the 
sick  person  to  some  one  else  by  kissing  or  by  handling  any  object  used  by 


AIR  AND  HEALTH  65 

the  sick  person.  In  the  case  of  diphtheria  the  bacteria  are  often  left  on 
the  rims  of  drinking-cups,  and  for  that  reason,  as  well  as  others,  it  is  well  to 
have  a  law  against  the  use  of  the  public  drinking-cup.  Diphtheria  and  tuber- 
culosis may  also  be  spread  by  the  medium  of  contaminated  milk.  Tuber- 
culosis is  especially  apt  to  be  spread  in  this  way,  because  cows  not  infre- 
quently have  this  disease  and  give  off  the  bacteria  in  their  milk.  Babies 
are  especially  apt  to  get  intestinal  tuberculosis,  and  there  is  excellent  reason 
for  believing  that  in  the  great  majority  of  such  cases  this  disease  has  been 
caused  by  infected  milk.  It  is  therefore  imperative  that  young  children 
should  be  given  milk  of  the  very  best  grade. 

.  How  to  care  for  the  sick.  The  facts  already  mentioned  about 
keeping  the  body  in  good  condition  apply  to  every  one.  There 
are  some  special  facts  that  those  who  have  to  take  care  of  sick 
persons  should  know.  It  is  quite  safe,  providing  one  follows  cer- 
tain rules,  to  care  for  a  consumptive  or  a  person  suffering  from 
pneumonia  or  diphtheria.  Cleanliness  is  the  most  important  thing. 
This  involves  an  understanding  of  how  to  destroy  the  bacteria 
that  the  sick  person  gives  off,  before  they  have  an  opportunity  of 
entering  the  body  of  another  person.  In  coughing  or  sneezing 
the  droplets  of  moisture  that  are  expelled  are  very  apt  to  contain 
the  living  organisms.  Some  of  them  may  even  float  in  the  air 
for  a  distance  of  several  feet  from  the  person  who  sent  them  out. 
Whatever  the  disease  may  be  that  your  patient  is  suffering 
from,  certain  rules  for  his  care  should  be  followed. 

1 .  Keep  the  dishes  and  silver  which  he  uses  separate  from  those 
of  the  rest  of  the  family.    Wash  them  always  in  boiling  water. 

2.  See  that  the  sick  room  receives  as  much  fresh  air  and  sun- 
light as  possible. 

3.  If  there  is  any  danger  of  infection  by  the  organisms  being 
carried  through  the  air,  keep  a  sheet  wet  with  a  disinfectant 
hanging  in  front  of  the  doorway. 

4.  Disinfect  all  discharges  from  the  body. 

Antiseptics  and  germicides.  Much  might  be  written  as  to  the 
use  of  antiseptics  and  germicides,  substances  having  the  power 
either  to  weaken  or  kill  bacteria,  and  the  methods  of  sterilizing 
dishes,  knives,  forks,  clothing,  etc.,  that  have  been  used  by  the 
patient.  The  subject  offers  an  excellent  opportunity  for  a  special 
project. 


66  THE  AIR  AND  HOW  WE  tfSE  IT 

By  antiseptics  we  mean  those  substances,  like  hydrogen  per- 
oxide, mercuric  chloride,  iodine,  carbolic  acid,  etc.,  which  in 
weakened  solutions  do  not  harm  the  outer  defenses  of  the  body, 
although  they  are  able  either  to  kill  or  at  least  weaken  the  bacteria 
found  there.  Such  substances  may  therefore  be  applied  directly 
to  the  human  body.  Germicides  are  stronger  substances.  They 
may  be  the  same  substances  as  antiseptics  only  in  stronger  solu- 
tions or  they  may  be  entirely  dirTerenTsubstances,  which  are  not 
safe  to  use  upon  the  body.  They  are  employed  to  kill  the  bacteria 
which  have  been  given  off  from  the  patient.  Such  materials  as 
formalin,  chloride  of  lime,  and  the  other  substances  already  men- 
tioned are  examples  of  germicides. 

The  most  common  method  of  sterilization  is  to  place  the  ma- 
terials to  be  sterilized  in  boiling  water  or  steam  for  fifteen  or 
twenty  minutes. 

If  at  any  time  you  have  to  help  take  care  of  a  sick  person  the 
doctor  will  doubtless  tell  you  just  what  is  to  be  done  so  that  you 
will  not  be  in  great  danger  of  getting  the  disease.  Doctors  and 
nurses  have  to  come  into  contact  with  sick  people  a  great  deal, 
and  yet  they  almost  always  are  able  to  avoid  diseases  by  taking 
just  such  precautions  as  we  have  mentioned. 

What  the  community  can  do  to  prevent  illness.  There  are 
many  things  that  communities  can  do.  We  shall  mention  only 
a  few.  They  should  have  laws  which  should  specify  just  how 
tenement  houses  must  be  constructed  so  as  to  insure  proper  ven- 
tilation. The  community  should  provide  through  free  hospitals 
and  dispensaries  for  the  care  and  treatment  of  those  who  cannot 
afford  to  pay  for  the  services  of  physicians.  It  should  quarantine 
the  sick  who  have  contagious  diseases  so  that  the  diseases  will 
not  be  spread.  It  should  provide  for  the  education  of  the  people, 
giving  the  reasons  why  spitting  should  be  prohibited  and  why 
such  a  thing  as  the  public  drinking-cuf)  should  be  abolished. 

INDIVIDUAL  PROJECTS 

Working  projects: 

1.  Demonstrate  how  a  vacuum  cleaner  works.     Write  to  a  manufacturer  for 
a  descriptive  catalogue. 

2.  Demonstrate  how  a  carpet  sweeper  works.     Write  to  a  manufacturer  for 
a  descriptive  catalogue. 


AIR  AND  HEALTH  67 

Reports: 

1.  Additional  facts  about  bacteria. 

Bacteria,  Yeasts,  and  Molds.     W.  H.  Conn.     D.  Appleton  &  Co. 
"How  Bacteria  Were  First  Seen."     Scientific  American  Supplement, 

March  4,  1916. 

Preventable  Diseases.     Woods  Hutchinson.     Houghton  Mifflin  Co. 
Primer  of  Sanitation.     John  W.  Ritchie.     World  Book  Co. 
The  Story  of  Germ  Life.     W.  H.  Conn.     D.  Appleton  &  Co. 
Wonders  of  Science.     Eva  M.  Tappan.     Houghton  Mifflin  Co. 

2.  Materials  found  in  dust. 

Dust  and  its  Dangers.     T.  P.  Prudden.     G.  P.  Putnam's  Sons. 
The  Kingdom  of  Dust.    J.  G.  Ogden.     Popular  Mechanics  Co.,  Chicago. 
"Measuring  the  Dust  in  the  Air."     Scientific  American  Supplement, 
July  15,  1916. 

3.  How  culture  media  are  prepared  for  growing  bacteria  in  the  laboratory. 
(See  bacteriology  textbook.) 

4.  Disinfectants  and  their  uses.     (See  bacteriology  textbook.) 

5.  Robert  Koch,  the  discoverer  of  the  tubercle  bacillus.     (See  bacteriology 
textbook.) 

6.  How  my  town  fights  tuberculosis.     Interview  the  Board  of  Health. 

BOOKS  THAT  WILL  HELP  YOU 

American  Red  Cross  Textbook  on  Elementary  Hygiene  and  Home  Care  of  the  Sick, 

J.  A.  Delano.     Blakiston. 

Cause  and  Cure  of  Colds.     W.  S.  Sadler.     McClurg. 
Consumption.     Metropolitan  Life  Insurance  Co. 
Good  Health.     Frances  Gulick  Jewett.     Ginn  &  Co. 
Handbook  of  Health.     Woods  Hutchinson.     Houghton  Mifflin  Co. 
How  to  Live.     Fisher  and  Fisk.     Funk  &  Wagnalls. 
Reports  of  the  New  York  State  Ventilation  Commission. 
"Sunlight,  a  Necessity  for  the  Maintenance  of  Health."    Scientific  American 

Supplement,  May  6,  1916. 
Town  and  City.     Frances  Gulick  Jewett.     Ginn  &  Co. 


UNIT  II 
WATER  AND  HOW  WE  USE  IT 


PROJECT  V 
WATER  IN  OUR  HOUSES 

Water  a  necessity  of  life.  Water,  because  it  is  such  a  com- 
mon thing,  is  often  not  appreciated.  We  are  so  accustomed  to 
find  it  directly  at  hand  whenever  we  are  thirsty  or  wish  to  wash 
our  faces  and  hands,  that  we  usually  do  not  stop  to  think  how  very 
necessary  it  is,  not  only  for  our  comfort  and  well-being,  but  for  life 
itself.  All  life,  both  plant  and  animal,  is  directly  dependent 
for  its  very  existence  upon  a  supply  of  water.  Without  it  all 
life-activities  would  soon  cease;  man  and  other  animals  would  soon 
die;  vegetation,  the  source  of  animal  food,  would  wither;  and  the 
earth  would  become  fruitless  and  barren. 

Because  of  this  dependence  of  man  upon  an  abundant  water- 
supply,  the  history  of  the  development  of  civilization  may  almost 
be  read  by  tracing  out  the  means  by  which  man  has  obtained  water. 
When  he  was  in  a  savage  state,  he  sought  water  in  much  the  same 
haphazard  way  in  which  he  sought  his  food.  Later  he  learned 
how  to  dig  wells  and  to  make  reservoirs  in  which  to  keep  water  for 
times  of  drought.  Now,  in  this  age  of  twentieth-century  civiliza- 
tion, when  people  live  together  in  great  communities,  vast  engi- 
neering problems  must  often  be  solved  in  order  to  provide  an 
abundant,  pure  water-supply.  We  find  huge  reservoirs  for  the 
storage  of  water  which  has  been  brought  to  them  from  sources 
many  miles  distant.  These  reservoirs  are  in  turn  connected  with 
private  homes  by  means  of  aqueducts  and  pipes.  All  this  has  been 
done  because  man  has  been  made  to  realize,  from  an  experience 
covering  hundreds  and  thousands  of  years,  that  water  is  essential 
to  his  life  and  happiness. 


WATER  IN  OUR  HOUSES  69 

The  human  body  needs  water.  Water  is  needed  by  man  in 
many  different  ways  for  carrying  on  life-activities,  (i)  He  needs 
water  to  help  make  his  body.  We  can  understand  this  need  of  the 
body  for  water  when  we  realize  that  more  than  two  thirds  of  the 
human  body  is  composed  of  water.  (2)  Food  must  be  dissolved, 
that  is,  turned  into  a  liquid,  before  it  can  really  become  part  of 
the  body  and  help  to  make  the  blood  and  other  body  substances. 
(3)  Water  is  also  needed  to  get  rid  of  waste  materials  that  are 
made  in  the  body.  This  is  just  as  important  a  process  as  the  tak- 
ing in  of  food.  The  wastes  must  be  in  a  dissolved  form  before 
they  can  be  passed  out  of  the  body,  and  water  helps  to  put  them 
in  this  form. 

The  problems  of  this  chapter  deal  with  your  supply  of  water  at 
home.  If  they  do  not  apply  to  your  own  conditions,  can  you  not 
devise  similar  problems  which  will  help  you  to  a  thorough  under- 
standing of  the  water-supply  of  your  home  and  of  your  commu- 
nity? Make  investigations  yourself ;  talk  the  matter  over  with 
your  father  and  with  others  who  understand  the  situation.  Do 
not  be  content  to  read  about  how  other  people  get  their  water  in 
other  places ;  find  out  exactly  how  you  get  your  water. 

If  you  live  in  a  large  town  or  in  a  city,  you  will  enjoy  a  trip  to 
the  pumping  station  with  the  class,  with  your  father  and  mother, 
or  with  a  group  of  friends.  Suggestions  for  such  a  trip  are  given 
in  problem  I .  You  may  find  how  the  water  has  been  brought  into 
your  house  for  your  use  by  working  out  problems  4,  5,  and  6.  If 
you  have  a  hot-water  system  at  home,  you  will  understand  how  it 
works  after  you  have  performed  problems  7,  8,  9,  and  10.  You 
can  learn  how  to  purify  water  by  trying  problems  2  and  3;  how 
water  helps  us  in  cooking  by  trying  problems  II,  12,  and  13;  and 
the  differences  in  water  by  trying  problem  14. 

Many  other  problems  about  water-supply  are  of  great  interest. 
Cities,  States,  and  the  Federal  Government  all  employ  experts 
who  help  in  furnishing  a  pure  supply  of  water  to  the  people  of  the 
Nation.  Many  such  employees  have  spent  years  in  preparing  for 
their  work.  In  high  school  they  have  studied  physics  and  chem- 
istry to  learn  the  general  principles;  and  then,  in  college  or  tech- 
nical school,  have  studied  bacteriology  to  find  out  how  to  recog- 


70  WATER  AND  HOW  WE  U&E  IT 

nize  impurities;  or  engineering,  to  find  out  how  to  get  the  water 
from  its  source  to  the  place  where  it  is  needed.  Perhaps  some  of 
you  may  one  day  do  the  same  kind  of  work.  At  any  rate,  you  can 
learn  something  of  what  has  been  done  along  this  line,  and  report 
what  you  have  learned  to  the  others  in  the  class.  The  individual 
projects  on  page  93  will  give  you  some  suggestions. 

PROBLEMS 
PROBLEM  i:  A  TRIP  TO  THE  PUMPING  STATION  AND  WATERWORKS  TO 

LEARN  ABOUT  THE  ClTY  WATER-SUPPLY. 

Directions: 

At  the  time  of  your  visit  to  the  waterworks  find  the  answers  to  the  fol- 
lowing questions  about  the  water-supply  of  your  town  or  city. 

1.  Where  does  the  water  come  from? 

2.  How  is  it  brought  to  the  pumping  station? 

3.  Is  there  a  reservoir  or  standpipe?     For  what  purpose? 

4.  How  does  the  water  get  up  into  the  reservoir? 

5.  What  precautions  are  taken  to  prevent  impurities  in  the  water? 

6.  How  are  the  water  mains  and  other  pipes  kept  from  freezing? 

7.  In  case  of  a  fire  in  the  town,  how  high  can  water  be  thrown  from  a 
hydrant  without  an  engine? 

Summary: 

Write  a  letter  to  a  friend  who  lives  in  the  country  and  explain  how  you 
get  your  water-supply. 

PROBLEM  2 :  To  COMPARE  THE  PURITY  OF  TAP  WATER  AND  BOILED  WATER. 

Directions: 

On  two  Petri 1  dishes  filled  with  sterilized  nutrient  agar,  drop  with  a 
sterilized  dropper  an  equal  number  of  drops  of  boiled  water,  and  water 
from  your  city  supply.  Set  the  dishes  aside  in  a  warm  place  and  examine 
from  day  to  day. 

Compare  the  number  of  colonies  of  bacteria  that  develop,  as  shown  by 
spots  on  the  agar. 

Conclusion: 
Which  kind  of  water  contains  fewer  bacteria? 

PROBLEM  3 :  To  PURIFY  WATER  BY  DISTILLING. 

Directions : 

Set  up  a  distilling  apparatus  as  shown  in  the  diagram.  Distil  water 
which  has  been  colored  in  some  way. 

1  See  Suggestions  for  Teachers. 


WATER  IN  OUR  HOUSES  71 

• 

If  a  regular  distilling  apparatus  is  not  in  the  school,  an  apparatus  may 
be  devised  by  using  two  round  pans  and  a  round  cake-tin  with  a  cone  in  the 
center,  as  shown  in  figure  41.  With  stout  shears  slit  the  cone  about  a  third 


FIG.  40.  A  distilling  apparatus.    Explain  why  the  vapor  which  passes  out  of 
the  upper  flask  condenses  before  it  reaches  the  lower. 

of  the  way  down  and  turn  back  the  flaps.  This  should  allow  the  three  tins 
to  fit  firmly  together  as  shown  in  the  diagram.  Fill  the  lower  tin  about  half 
full  with  water  containing  some  coloring  matter. 
Fit  the  cake-tin  over  it  to  collect  the  condensed 
steam.  Fit  the  other  tin  over  the  top  and  fill 
with  cold  water.  Place  the  whole  apparatus  on 
the  stove,  or  over  a  gas-burner. 

Listen  for  the  sound  of  boiling.  In  which  pan 
is  the  water  boiling?  Is  the  water  in  the  upper 
tin  cold  or  hot  when  boiling  is  first  heard? 

Boil  for  at  least  fifteen  minutes.  Separate  the 
tins.  What  is  in  the  middle  tin?  Explain. 

What  is  in  the  lower  tin? 


FIG.  41.  A  home-made 
distilling  apparatus. 


Conclusions: 

1.  Wrhat  passes  off  when  water  is  boiled? 

2.  When  water  containing  impurities  is  boiled,  what  becomes  of  the 
impurities? 

3.  Is  boiled  water  safe  to  drink?     Explain. 


WATER  AND  HOW  WE  USE  IT 


PROBLEM  4 :  To  TRACE  THE  COLD-WATER  PIPING  SYSTEM  OF  MY  HOUSE. 
Note:  Perhaps  your  father  will  help  you  with  this  problem. 

Directions; 

1.  Find  out  where  the  water  enters  your  house  from  the  city  pipes.     Is 
it  possible  to  shut  off  the  water-supply  from  the  house?    Why  might  it  be 
necessary  to  shut  off  the  supply? 

2.  Trace  the  main  supply  pipe.     Where  does  it  lead?     Is  it  the  same 
size  as  the  other  water  pipes? 

3.  Count  and  locate  the  number  of  cold-water  faucets  in  the  house. 
Is  there  any  connection  between  the  number  of  faucets  and  the  amount 
of  the  water  bill? 

Summary; 

Do  you  understand  the  different  parts  of  the  cold-water  piping  system 
so  that  you  can  adjust  any  part  which  may  get  out  of  order? 

PROBLEM  5:  WHY  DOES  WATER  RISE  IN  PIPES? 

Directions: 

Arrange  an  apparatus  like  the  figure,  consisting  of  three  lamp  chimneys, 
rubber  stoppers,  pieces  of  glass  tubing,  and  rubber  tubing.  Let  three  mem- 
bers of  the  class  support  the 
chimneys  upright.  Let  an- 
other member  pour  water  into 
one  of  the  chimneys.  What 
happens  in  the  other  chim- 
neys? 

Hold  A  a  little  higher  than 
B  and  C.     What  happens? 

Hold    B    a    little    higher. 
What  happens? 

Hold  C  a  little  higher.     Is 
the  result  the  same? 

Empty  the  water  from  the 
apparatus.  Replace  chimney 
A  with  a  piece  of  glass  tubing 
drawn  out  to  a  jet  at  one  end. 
Run  water  into  C,  holding  the  jet  higher  than  the  chimney  tops.  What 
happens? 

Put  your  finger  over  the  end  of  the  jet,  and  lower  the  jet  to  the  level  of 
the  bottom  of  the  chimneys.    Remove  your  finger.    Explain  what  happens. 

Summary; 
What  is  the  level  of  water  in  connecting  pipes? 


FIG.  42.  Water  level  in  connecting  pipes. 


WATER  IN  OUR  HOUSES 


73 


Questions: 

1.  Why  does  the  waiter  rise  in  the  water  pipes  in  your  house? 

2.  What  causes  water  to  flow  from  a  faucet? 

3.  What  effect  has  friction  in  the  pipes  on  the  force  with  which  water 
flows  from  a  faucet? 

4.  Explain  the  flow  of  a  fountain. 


PROBLEM  6 :  How  DOES  A  WATER  FAUCET 
WORK? 

Directions: 

Secure  faucets  of  different  types  from  a 
plumbing  house.  It  is  sometimes  possible 
to  get  samples  which  are  sawed  in  parts 
for  demonstration  purposes.  Study  also 
the  faucets  in  your  own  house. 

1.  The  screw  type. 

What  is  the  effect  when  the  handle 
is  screwed  down? 

What  is  the  effect  when  the  handle 
is  screwed  up? 

What  are  the  advantages  and  dis- 
advantages of  this  type  of  faucet? 

How  may  a  new  washer  be  inserted 
when  necessary? 

2.  The  compression  type. 

How  far  will  the  handle  turn? 

What  is  the  effect  when  the  handle 
is  turned  in  the  other  direction? 

What  prevents  the  water  from  flow- 
ing when  the  faucet  is  closed? 

What  are  the  advantages  and  dis- 
advantages of  this  type  of  faucet? 

3.  The  spring  type. 

What  is  the  effect  when  the  handles 
are  brought  together? 

What  keeps  the  water  from  flowing 
when  the  faucet  is  closed? 

What  are  the  advantages  and  dis- 
advantages of  this  type  of  faucet? 


FIG.  43.  Three  types  of  water 
faucets.  A ,  the  screw  type.  B,  the 
compression  type.  C,  the  spring 
type. 


Summary: 

Make  a  careful  drawing  in  your  notebook  of  the  kind  of  faucet  used  in 
your  home,  and  explain  how  it  works. 


74 


WATER  AND  HOW  WE  USE  IT 


PROBLEM  7:  How  is  MY  HOUSE  SUPPLIED  WITH  HOT  WATER? 

Directions: 

Examine  the  hot-water  tank  or  "boiler"  in  your  house.  How  many 
pipes  are  connected  with  it? 

Feel  the  pipes  while  the  water  is  being  heated.  Which  are  carrying  cold 
water?  Which  are  carrying  hot  water? 

Find  the  pipe  which  carries  the  cold  water  from  the  city  water-supply 
into  the  tank. 

Find  the  pipe  which  carries  the  cold  water  out  of  the  tank  to  be  heated. 
Where  is  the  water  heated?  What  supplies  the  heat? 

Find  the  pipe  which  carries  the  hot  water  back  into  the  tank.  Does  it 
enter  the  tank  at  the  bottom,  the  side,  or  the  top? 

Find  the  pipe  which  carries  the  hot  water  to  the  hot-water  faucets  in 
different  parts  of  the  house. 

Feel  the  sides  of  the  tank.  Where  is  it  hottest?  coolest?  Can  you 

account  for  the  difference  in  tem- 
perature? 

Summary; 

Make  a  careful  drawing  of  the 
hot-water  heater  in  your  home 
with  its  connections.  Label  all 
its  parts. 

PROBLEM  8:  How  is  WATER  AF- 
FECTED BY  HEATING? 

Directions: 

Part  i.  Pour  water  into  a  flask 
until  it  is  full.  Put  a  little  coloring 
in  the  water.  Close  the  flask  with 
a  one-holed  rubber  stopper  fitted 
with  a  glass  tube  about  a  foot 
long. 

Heat  the  flask.    What  happens 
to  the  water?     Why? 
Part  2.  Balance  two  empty  flasks  on  delicate  scales.     Pour  cold  water 
into  one  flask,  and  an  equal  volume  of  hot  water  into  the  other.     Do  the 
flasks  still  balance?     Explain  the  reason. 

Conclusions: 

1.  How  does  heating  affect  the  volume  of  water? 

2.  How  do  equal  volumes  of  hot  wrater  and  cold  water  compare  in  weight? 

Questions; 

i.  Why  does  water  sometimes  flow  out  of  a  tank  overflow  pipe  when  a 
fire  is  started  in  the  kitchen  range? 


FIG.  44.  Which  jar  contains  cold  water  ? 


WATER  IN  OUR  HOUSES 


75 


2.  ^  Why  does  water  sometimes  overflow  from  the  radiator  of  an  auto- 
mobile after  the  engine  has  been  running  some  time? 

PROBLEM  9:  How  is  THE  WATER  IN  A  HOT-WATER  TANK  HEATED? 
Directions; 

A  model  of  a  hot-water  tank  may  be  made  as  follows : 

Solder  one  metal  tube  to  the  bottom  of  an  ether  can,  another  to  the  side, 
and  another  to  the  top.  By 
bending  glass  tubing  and  con- 
necting it  with  rubber  tubing 
arrange  an  apparatus  like  the 
diagram.  Use  a  funnel  tube 
and  stop-cocks. 

What  part  of  your  appara- 
tus represents  the  tank?  the 
stove?  the  pipes  to  and  from 
the  stove?  the  hot-water  pipes? 
a  hot-water  faucet?  the  over- 
flow tank? 

Fill  the  apparatus  with  water, 
making  sure  that  the  can  and 
tubes  are  entirely  full  and  free 
from  bubbles,  and  the  bulb  of 
the  funnel  tube  is  half  full. 
Have  the  faucet  stop-cock 
closed  and  the  overflow  stop- 
cock open. 

Heat  the  corner  of  the  glass 
tubing.  Drop  a  few  grains  of 
carmine  or  other  coloring  mat- 
ter into  the  top  of  the  funnel 
tube. 

Watch  carefully.     Explain  everything  that  happens. 

After  several  minutes,  open  the  faucet  stop-cock.  What  happens?  Explain. 

Make  a  careful  drawing  of  the  apparatus.     Show  by  arrows  the  move- 
ment of  the  water. 

Question; 

How  is  a  fire  in  a  stove  able  to  heat  all  the  water  in  a  tank  some  distance 
away? 

PROBLEM  10:  To  TRACE  THE  HOT-WATER  PIPING  SYSTEM  OF  A  HOUSE. 

Directions ; 

How  is  water  heated  in  your  house? 

Find  the  pipe  which  carries  the  heated  water  from  the  tank. 


FIG.  45.  A  model  of  a  hot-water  tank. 


76 


WATER  AND  HOW  WE  U&E  IT 


How  many  hot-water  faucets  are  in  the  house?  Trace  the  pipes  which 
supply  each  faucet. 

Is  it  necessary  to  run  the  water  for  some  time  before  hot  water  runs 
from  the  faucet?  Why? 

1$  the  pressure  which  forces  water  out  of  the  faucets  furnished  by  a  tank 
at  the  top  of  the  house  or  by  the  city  system? 

Summary: 

Make  a  careful  diagram  showing  the  hot-water  connections  in  your 
kitchen. 

Questions: 

1.  Why  are  water-supply  tanks  placed  as  high  as  possible  in  houses? 

2.  What  are  the  disadvantages  in  having  water  pipes  located  next  to  the 
outside  walls  of  a  house? 

PROBLEM  1 1 :  WHAT  CHANGES  TAKE  PLACE  IN  EGG-WHITE  WHILE  IT  is 

BEING  COOKED  IN  WATER? 

Directions: 

Fill  a  beaker  or  small  stewpan  about  two  thirds  full  of  water.  Place  it 
on  a  ring-stand.  (See  diagram.) 

Pour  egg-white  into  the  bottom  of  a  test-tube. 
Clamp  the  test-tube  so  that  its  bottom  is  half  an  inch 
above  the  bottom  of  the  beaker,  and  the  level  of  the 
water  stands  above  the  top  of  the  egg-white.  Clamp 
a  chemical  thermometer  with  its  bulb  in  the  egg- 
white,  slightly  above  the  bottom  of  the  test-tube. 
Heat  the  water  in  the  stewpan. 

Watch  carefully  all  changes  that  take  place. 

What  is  the  temperature  when  the  first  visible 
change  occurs?  Is  the  water  boiling? 

What  is  the  temperature  when  the  egg-white  be- 
comes jelly-like  throughout?  Is  the  water  boiling? 

What  is  the  temperature  when  the  water  boils? 

Remove  the  egg-white  from  the  beaker.    What  is 
its  appearance? 
Question: 

How  does  the  apparatus  used  in  this  experiment 
differ  from  a  double  boiler?     What  are  the  advantages  of  a  double  boiler? 


FIG.  46.   Cooking  egg- 
white  in  a  test-tube. 


PROBLEM  12:  WHAT  is  THE  EFFECT  OF  COOKING  MEAT  IN  DIFFERENT 

WAYS  IN  WATER? 
Directions: 

Fill  three  glass  beakers  two  thirds  full  of  cold  water. 

Into  the  first  beaker  put  a  small  piece  of  meat.    Allow  it  to  stand. 


WATER  IN  OUR  HOUSES  77 

Into  the  second  beaker  put  a  small  piece  of  meat.  Heat  it  over  a  flame. 
After  the  water  reaches  the  boiling  point,  boil  five  minutes. 

Heat  the  water  in  the  third  beaker  to  the  boiling  point.  Then  throw  in 
a  small  piece  of  meat.  Boil  five  minutes. 

Remove  the  beakers  from  the  flame,  and  compare  the  appearance  of  the 
meat  and  the  water  in  the  three  beakers. 

Which  treatment  has  removed  most  juices  from  the  meat? 

Which  treatment  has  been  best  to  keep  the  juices  in  the  meat? 

Remove  the  three  pieces  of  meat  from  the  water.  Cut  each  piece,  as 
well  as  a  piece  of  raw  meat. 

Which  treatment  has  softened  the  meat  fibers  most? 

Summary: 

Name  two  ways  in  which  water  helps  us  to  cook  meat. 
Questions: 

1.  Which  of  the  treatments  used  in  this  experiment  would  be  best  for 
making  soup?     Why? 

2.  Which  would  be  best  for  boiling  meat?     Why? 

PROBLEM  13:  How  DOES  WATER  HELP  us  IN  COOKING  STARCHY  FOODS? 
Directions: 

Pare  two  small  potatoes.  Note  the  appearance  of  the  pared  surface. 
Drop  one  potato  into  boiling  water.  Let  it  boil  gently  for  about  half  an 
hour.  Test  it  occasionally  with  a  fork,  and  note  any  changes  which  take 
place  in  it. 

While  the  potato  is  boiling,  cut  the  thinnest  possible  slice  from  the  other 
potato.  Place  a  drop  of  iodine  on  it.  (Iodine  turns  starch  grains  blue  or 
purple.) 

Watch  carefully  for  any  changes.  Can  the  iodine  reach  the  starch 
grains  immediately? 

If  possible,  examine  the  thin  slice  with  a  compound  microscope.  Can 
you  see  the  cells  of  the  potato?  Can  you  see  the  grains  of  starch  within 
the  cells?  Sketch  their  appearance. 

When  the  potato  is  done,  remove  it  from  the  boiling  water.  How  has 
its  appearance  changed?  What  seems  to  have  come  from  the  cells? 

Test  a  thin  slice  with  iodine.     Account  for  the  action. 

Examine  the  stained  slice  of  boiled  potato  with  the  compound  micro- 
scope. Are  the  starch  grains  now  included  within  unbroken  cell  walls? 
Can  you  see  the  shape  of  the  starch  grains? 

Summary: 

1.  What  is  the  action  of  boiling  water  on  starch  grains? 

2.  What  is  the  action  on  cell  walls  when  potatoes  are  boiled? 


78  WATER  AND  HOW  WE  USE  IT 

PROBLEM  14:  Is  THE  WATER  AT  HOME  HARD  OR  SOFT? 

Directions: 

Part  i.  Fill  a  pan  with  warm  water  from  the  faucet.  Shake  some  soap 
in  the  water.  Do  suds  appear  very  soon?  If  so,  the  water  is  soft. 

Does  a  whitish  scum  appear?     If  so,  the  water  is  hard. 

Part  2.  If  the  water  is  hard,  try  the  following  tests: 

Shake  soap  in  water  that  has  been  boiled.  Do  suds  appear  at  once? 
Temporary  hard  water  becomes  soft  after  boiling,  while  permanent  hard 
water  remains  hard.  Is  the  water  still  hard? 

Dissolve  soda  ash,  washing  soda,  or  borax  in  the  hard  water.  Now  add 
the  soap.  Is  the  water  now  hard  or  soft? 

Conclusion: 
What  kind  of  water  have  you  at  home? 

Question: 

How  may  hard  water  be  softened? 

Sources  of  our  drinking-water.  Even  to  primitive  man  the 
necessity  for  obtaining  a  supply  of  pure  water  must  have  been 
apparent.  When  in  the  course  of  the  development  of  mankind 
people  began  to  live  in  tribes,  it  was  usually  their  custom  to  settle 
along  the  banks  of  some  stream  and  then  apportion  strips  of  land 
to  families,  each  family  having  some  land  bordering  on  the  stream. 
They  would  cultivate  the  fields  in  a  simple  way,  use  the  forests 
for  wood,  and  after  a  time  migrate  to  another  district  where  they 
could  have  the  same  general  conditions  that  were  necessary  for 
existence.  If  they  did  not  live  along  the  banks  of  streams,  they 
were  obliged  to  settle  near  lakes  or  springs  or  else  dig  wells,  and 
thus  tap  underground  springs  and  streams.  It  was  not  until 
comparatively  recent  years  that  reservoirs  were  generally  con- 
structed for  the  storage  of  water,  although  some  were  built  in 
ancient  times  in  India  and  a  few  other  places. 

New  York  City  may  be  taken  as  an  example  of  how  a  modern  city  has 
been  forced  to  solve  an  increasingly  difficult  problem  in  obtaining  an 
abundant  supply  of  pure  water.  Starting  as  a  small  town,  New  York 
was  at  first  able  to  meet  the  demands  of  its  citizens  for  water  by  using  the 
springs  and  streams  near  at  home  and  by  digging  wells.  As  the  city  has 
increased  in  size,  it  has  been  necessary  to  go  farther  and  farther  away  from 
the  city  in  order  to  get  enough  water.  The  Catskill  Aqueduct  now  brings 
the  water  from  more  than  a  hundred  miles  away. 


WATER  IN  OUR  HOUSES 


79 


Pure  water  and  impure.  Not  only  must  the  water-supply  be 
abundant;  it  must  be  pure.  Chemists  connected  with  a  city 
water  department  are  constantly  testing  the  water  to  make  sure 
that  no  impurities  have  entered  it.  If  any  impurities  are  found, 
the  water  is  treated  in  such  a  way  as  to  render  them  harmless. 


FIG.  47.  How  water  is  carried  to  the  city  from  distant  reservoirs 
in  the  country. 

(From  Hutchinson's  Handbook  of  Health.') 


Water  may  be  made  impure  in  a  number  of  ways,  (i)  It  may  have 
harmful  substances  dissolved  in  it,  such  as  factory  waste.  (2)  It 
may  have  fine  materials  suspended  in  it,  such  as  particles  of  mud. 
(3)  It  may  contain  bacteria  that  cause  disease.  It  is  this  last 
possibility  that  needs  especially  to  be  guarded  against.  Often  it 
is  impossible  by  merely  looking  at  or  tasting  the  water  to  tell 
whether  it  is  safe  to  drink.  The  only  sure  way  is  to  have  it  ex- 
amined chemically  and  bacteriologically  for  the  purpose  of  finding 
whether  poisonous  substances  and  disease-producing  bacteria  are 
present. 

Typhoid  fever,  a  disease  often  spread  by  impure  drinking-water. 
Typhoid  fever,  although  often  spread  in  other  ways,  is  probably 


8o  WATER  AND  HOW  WE  USE  IT 

more  often  spread  by  contaminated  water  than  in  any  other  man- 
ner. It  is  caused  by  certain  kinds  of  bacteria,  known  as  typhoid 
bacilli,  which  always  enter  the  body  through  the  mouth  either  in 
the  food  that  is  eaten  or  the  water  that  is  drunk.  (See  figure  36  on 
page  52.)  Typhoid  is  spread  by  means  of  the  wastes  of  the  patient. 
Food  and  water  can  only  be  contaminated  by  being  made  filthy 
through  receiving  either  directly  or  indirectly  the  discharges  that 
have  come  from  the  body  of  a  person  sick  with  this  disease.  These 
discharges  contain  bacteria  which  produce  the  disease.  It  is  there- 
fore extremely  necessary  for  the  nurse  or  person  taking  care  of  the 
patient  to  disinfect  this  material  just  as  soon  as  possible  after 
it  leaves  the  body.  If  this  is  thoroughly  done,  the  disease  can- 
not be  spread.  If,  however,  through  carelessness  on  the  part  of 
the  attendant,  flies  are  allowed  to  light  upon  the  discharges,  the 
bacteria  may  be  transferred  by  them  to  food,  and  so  cause  the 
disease  in  some  other  person.  If  the  infected  discharges  are  al- 
lowed to  enter  the  sewage,  the  bacteria  may  find  their  way  into 
drinking  water,  and  indirectly  into  milk,  oysters,  and  other  raw 
foods.  Although  this  disease  does  not  cause  nearly  as  many 
deaths  in  the  United  States  as  consumption  or  pneumonia,  never- 
theless it  is  one  of  the  most  common  diseases.  About  one  per- 
son out  of  ten  of  those  having  typhoid  fever  fails  to  recover. 
When  we  know,  for  instance,  that  about  twenty-five  thousand 
people  in  the  United  States  die  every  year  from  typhoid  fever, 
we  must  realize  that  those  twenty-five  thousand  deaths  meant 
that  there  were  about  two  hundred  and  fifty  thousand  people 
who  had  to  pay  the  doctors'  bills  and  who  were  probably  unable 
to  work  for  a  period  of  a  month  or  longer.  The  importance  of 
a  water-supply  free  from  any  danger  of  such  disease  cannot  be 
overestimated.  City  after  city  has  markedly  reduced  the  num- 
ber of  typhoid  fever  victims  by  improving  its  water-supply.  All 
members  of  the  army  and  navy  of  the  United  States  were  in- 
oculated against  typhoid  fever  at  the  time  of  the  Great  War,  with 
such  success  that  the  number  of  cases  were  very  few.  How  would 
it  be  possible  to  stamp  out  typhoid  fever  throughout  the  world  ? 
How  water  is  purified.  It  is  not  always  possible  easily  to  ob- 
tain pure  drinking  water.  In  small  towns  there  is  often  not  suf- 


WATER  IN  OUR  HOUSES  81 

ficient  money  to  build  reservoirs  and  carry  out  projects  of  this 
kind.  It  may  be  necessary  to  take  the  water  from  streams  that 
are  contaminated.  What  is  to  be  done  in  such  cases? 

If  there  is  doubt  as  to  the  purity  of  the  water,  each  householder 
must  take  measures  to  obtain  a  pure  supply  for  his  own  family. 
Distilled  water,  which  may  be  obtained  in  stores,  is  as  pure  as  water 
can  be.  Doctors  prescribe  it  for  certain  patients,  but  for  most 
people  it  is  not  necessary  to  drink  this  kind  of  water.  Distilled 
water  is  made  by  condensing  the  vapor  from  boiling  water  by 
passing  this  vapor  through  cooled  tubes,  where  the  condensed 
vapor  runs  out  as  water.  Any  impurities  which  the  water  may 
have  originally  contained  are  thus  left  behind  in  the  vessel  in 
which  the  water  was  boiled. 

An  excellent  way  of  purifying  water  in  the  home  is  to  boil  it, 
for  this  kills  any  bacteria  it  may  contain.  Boiled  water  has 
what  is  called  a  "  dead  "  taste.  This  may  be  partially  removed 
by  pouring  the  boiled  water  from  one  receptacle  into  another  so 
that  some  of  the  air  which  has  been  removed  by  boiling  may 
get  back  again,  thus  restoring  to  the  water  its  pleasing  taste. 
Filters  that  are  commonly  used  in  homes  for  purifying  water  are 
usually  not  efficient,  since  they  permit  bacteria  to  pass  through 
them,  and  hold  back  only  the  coarser  materials  in  the  water, 
which  are  apt  to  be  harmless. 

Although  not  successful  in  a  household,  a  filter  may  be  used 
successfully  in  connection  with  the  water-supply  of  a  community. 
One  of  the  commonest  kinds  of  filters  is  the  sand  filter.  It  has 
been  found  that  water  which  has  passed  through  a  properly  con- 
structed sand  filter  is  almost  if  not  entirely  purified.  At  least  the 
harmful  bacteria  are  largely  removed  by  the  action  of  the  filter, 
and  the  water  is  thus  made  safe  to  drink.  Another  way  by  which 
a  town  or  city  may  purify  its  water  is  to  add  to  it  certain  chemicals 
which  in  small  amounts  do  no  injury  to  the  body,  but  are  able  to 
kill  disease-producing  bacteria.  These  chemicals  also  destroy 
any  harmful  dead  organic  matter  which  may  be  present.  Thus 
we  have  seen  that  four  successful  methods  may  be  used  to  purify 
the  water  which  we  drink:  (i)  distillation,  (2)  boiling,  (3)  the  use 
of  sand  filters,  (4)  the  use  of  chemicals. 


82  WATER  AND  HOW  WE  USE  IT 

Water  pressure.  Have  you  wondered  how  it  is  possible  for 
water  to  come  out  of  the  pipes  in  your  house  with  such  force?  If 
you  live  in  a  city  your  water  probably  comes  to  you  from  a  source 
many  miles  away.  It  is  sent  through  underground  pipes  and 
supplied  to  thousands  of  faucets.  The  pressure  which  forces  the 
water  out  is  furnished  by  water  stored  in  some  high  reservoir  or 
standpipe,  or  by  pumps. 

A  city  water-supply  must  be  under  pressure,  not  only  in  order 
that  the  water  may  be  used  in  the  upper  floors  of  tall  buildings, 
but  also  to  help  in  fighting  fires.  To  understand  how  a  standpipe 
may  furnish  pressure,  you  must  know  something  of  the  way  that 
water  behaves.  You  know  that  water  has  weight.  One  cubic 
foot  of  pure  water  weighs  62.5  pounds.  When  water  is  one  foot 
deep,  therefore,  it  presses  down  with  a  weight  of  62.5  pounds  on 
every  square  foot.  If  a  standpipe  100  feet  high  is  full  of  water,  the 
pressure  on  the  bottom  is  100  times  62.5  pounds,  or  6250  pounds 
on  every  square  foot. 

One  fact  to  be  remembered  about  water  pressure  is  that  the 
pressure  is  equal  in  all  directions.  Halfway  down  a  loo-foot  stand- 
pipe  the  pressure  on  each  square  foot  is  50  times  62.5,  or  3125 
pounds.  This  pressure  is  the  same  whether  it  is  exerted  down- 
wards, sidewise,  or  upwards.  The  water  presses  against  the  sides 
of  the  standpipe  with  just  as  much  force  as  it  presses  downwards. 
Engineers  must  reckon  on  such  a  sidewise  pressure  when  they 
build  standpipes,  in  order  to  make  the  walls  strong  enough  to 
stand  the  pressure. 

If  the  height  of  the  water  in  the  standpipe*  varies,  the  pressure 
in  the  pipes  leading  from  it  to  the  houses  also  varies.  Perhaps 
you  have  noticed  that  at  times  the  water  comes  from  the  faucets 
in  your  house  with  greater  force  than  at  other  times.  If  you  have 
a  standpipe  in  your  town,  you  can  account  in  this  way  for  some 
of  the  variation  in  pressure. 

It  may  not  be  evident  to  you  yet  why  the  water  rises  in  the  pipes 
in  your  house,  no  matter  how  high  above  the  ground  the  rooms 
are.  It  is  because,  as  stated  above,  water  presses  in  all  directions. 
The  pipes  in  your  house  are  connected  with  larger  pipes  in  the 
street,  and  thus  with  the  standpipe  or  reservoir.  If  the  pressure 


WATER  IN  OUR  HOUSES  83 

in  any  part  of  the  connecting  pipes  is  greater  than  in  other  parts, 
that  pressure  tends  to  push  down,  up,  and  sidewise  with  equal 
force,  and  thus  to  cause  a  movement  of  the  water.  If  an  opening 
is  given  the  water,  as  when  a  faucet  is  turned,  the  pressure  pushes 
the  water  up  and  out  of  the  faucet.  If  the  faucet  were  above  the 
level  of  the  water  in  the  standpipe,  no  water  would  flow  out. 
This  action  of  the  water  is  dependent  upon  the  principle:  water 
seeks  its  own  level.  (See  figure  42.) 

The  explanation  in  this  paragraph  for  the  water  pressure  in 
your  pipes  applies  only  if  your  community  has  an  elevated  res- 
ervoir of  some  kind.  In  some  places  the  water  is  pumped  di- 
rectly into  the  pipes.  Pressure  in  such  a  case  is  furnished  by 
the  pumps. 

Water-supply  systems.  The  source  of  the  water  which  is  sup- 
plied to  your  house  may  be  (i)  rain,  (2)  a  spring,  (3)  a  shallow 
well,  (4)  a  deep  driven  well,  (5)  an  underground  stream,  (6)  a 
mountain  stream,  (7)  a  large  river,  or  (8)  a  lake. 

In  Bermuda  the  only  source  of  drinking-water  is  the  rain. 
Most  houses  have  roofs  made  of  fluted  tiles,  so  arranged  as  to 
conduct  the  rainwater  into  a  cistern  at  the  side  of  the  house.  Rain- 
water is  not  especially  pure,  since  it  may  contain  impurities  from 
the  air. 

Springs  may  furnish  clear,  sparkling  water  which  yet  may  be 
impure.  Country  houses  often  obtain  their  water  from  springs. 
The  end  of  a  pipe  is  laid  in  the  spring;  the  water  is  pumped  by 
a  gasoline  engine  to  a  tank,  which  is  sometimes  placed  on  top  of 
the  house  or  barn ;  and  the  water  either  flows  from  the  tank  into 
pipes  by  its  own  weight  or  is  pushed  out  by  the  pressure  of  com- 
pressed air  in  the  top  of  the  tank.  Whether  water  comes  from 
springs,  wells,  or  streams,  the  pressure  in  a  rural  district  may  be 
obtained  easily  and  economically  by  pumping  it  thus  to  a  tank. 

Wells  are  unsafe  if  shallow,  especially  if  they  are  situated  near 
cesspools,  outhouses,  or  manure  piles.  Waste  matter  may  soak 
through  the  soil  and  run  into  the  well,  because  the  layers  of  soil 
and  rock  may  be  so  arranged  that  drainage  takes  that  direction. 
As  such  waste  matter  does  not  usually  soak  very  far  into  the 
ground,  deep  "  driven  "  wells  and  artesian  wells  are  not  likely 


84 


WATER  AND  HOW  WE  USE  IT 


to  contain  impure  water.  Some  towns,  as  well  as  separate  houses, 
get  their  water-supply  from  artesian  wells.  The  rock  is  bored  until 
a  porous  layer  is  reached  which  outcrops  on  some  distant  hillside. 
Since  water  seeks  its  own  level,  and  since  the  pressure  is  exerted 
in  every  direction,  the  water  may  be  forced  to  the  upper  floors  of 
houses  and  even  much  higher.  In  general,  surface  water,  whether 


FIG.  48.  A  farmhouse  system  by  which  water  is  pumped  from  a  shallow  well. 
(Courtesy,  Leader  Iron  Works.) 


obtained  from  wells  or  from  streams,  is  more  apt  to  contain  im- 
purities than  water  obtained  from  underground  streams  or  springs. 
The  water  of  mountain  streams  is  usually  pure,  especially  if 
the  region  is  uninhabited.  Several  large  cities  bring  their  water 
many  miles  through  aqueducts  from  distant  mountain  districts. 
The  water  usually  flows  to  the  city  because  of  its  own  weight. 
Such  a  system  is  therefore  called  a  gravity  system.  Los  Angeles, 


WATER  IN  OUR  HOUSES  85 

California,  and  Denver,  Colorado,  obtain  their  water  in  this  way. 
A  gravity  system  is  especially  fitted  for  a  mountainous  region. 

Cities  located  on  plains  must  usually  obtain  their  water  from 
lakes  or  rivers'.  Such  water  is  apt  to  be  impure,  and  should  al- 
ways be  filtered  before  entering  the  pipes.  In  most  cities  of  the 
plains  there  is  a  pumping  system,  whereby  the  water  is  pumped 
through  the  main  pipe  lines  into  the  houses.  Cities  on  the  Great 


FIG.  49.   Well  water  may  be  unsafe  to  drink. 


Lakes,  —  for  example,  Cleveland  and  Buffalo,  —  which  must  also 
empty  their  sewage  into  the  lake,  pipe  their  water  from  "  cribs  " 
five  miles  or  more  from  shore,  in  order  to  obtain  as  pure  water  as 
possible.  Chicago,  in  order  to  keep  its  water-supply  from  the 
lake  pure,  has  spent  great  sums  of  money  to  construct  the  "  drain- 
age canal  "  which  carries  its  sewage  away  from  the  lake  into  the 
Mississippi  River  system. 

In  hilly  parts  of  the  country  a  combination  of  the  gravity  and 
pumping  systems  are  used.  New  York  obtains  its  water  from 
the  Catskill  Mountains.  The  water  flows  through  the  aqueduct 
by  its  own  weight,  but  is  pumped  to  the  buildings.  Boston  ob- 
tains its  water  from  a  series  of  lakes  miles  away.  After  it  flows 
to  the  city  by  gravity,  it  is  pumped  either  directly  into  the  pipes 


86 


WATER  AND  HOW  WE  l!SE  IT 


to  the  houses,  or  to  standpipes  from  which  it  flows  to  the  houses 
by  gravity. 

A  house  piping  system.  The  water  pipes  in  a  house  may  be  di- 
vided into  the  cold-water  supply  pipes  and  the  hot-water  supply 
pipes.  The  cold  water  comes  directly  from  the  city  pipes  in  the 
street.  The  main  supply  pipe  has  several  branches  which  lead 
to  the  cold-water  faucets  and  the  closet  tanks.  If  the  cold-water 


FIG.  50.  A  water  system  dependent  on  both  gravity  and  pumping.  Notice  that  the 
tallest  building  has  a  small  standpipe  of  its  own  to  furnish  fire  protection.  Water  must 
be  pumped  to  this  tank. 

pipes  are  all  of  the  same  size,  the  turning-on  of  one  faucet  is  apt 
to  lessen  the  pressure  from  the  other  faucets.  To  prevent  this  the 
main  supply  pipe  should  be  larger  than  the  branches. 

Faucets  are  used  to  control  the  flow  of  water  from  the  pipes. 
Three  of  the  commonest  types  are  the  screw,  the  compression, 
and  the  spring.  (See  problem  6  on  page  73.) 

A  hot-water  heater.  The  hot-water  supply  is  usually  furnished 
by  a  device  in  the  house.  The  water  may  be  heated  by  circulating 
through  the  kitchen  range,  by  a  heating  coil  in  the  furnace,  or  by 
circulating  through  coils  heated  by  kerosene,  gas,  or  electricity. 

One  of  the  commonest  ways  of  heating  water  is  the  tank  or 
"  boiler  "  connected  with  the  kitchen  range.  (See  the  diagram.) 
In  order  to  understand  how  the  water  in  such  a  tank  is  heated, 
we  must  know  the  difference  in  behavior  between  hot  and  cold 
water.  First,  hot  water  is  lighter  than  cold  water.  A  quart  of  hot 
water  weighs  a  little  less  than  a  quart  of  cold  water.  The  tem- 
perature at  which  water  is  heaviest  is  4°  Centigrade,  or  about 
39°  Fahrenheit.  If  hot  and  cold  water  are  mixed,  the  heavier 
cold  water  presses  in  under  the  lighter  hot  water.  Therefore  hot 


WATER  IN  OUR  HOUSES 


water  rises.    A  circulation  is  thus  started,  by  which  in  time  all 

the  water  tends  to  be  heated 

equally.     Such  a   circulation 

is  known  as  convection.     (See 

page  75.) 

In    the   kitchen    hot-water 

tank  connected  with  a  range, 

the  water  is    heated    in    the 

water-front  or   water-back,  so 

named  according  to  the  part 

of  the  stove  where  the  coils 

are  located.    As  soon  as  the 

water  in  the  stove  is  heated, 

cold  water  presses  in  from  the 

lower  part  of  the  tank  and 

forces  the  heated  water  back 

into  the  tank.    In  the  tank  it 

rises  to  the   top.     Can   you 

understand  now  why  the  pipes 

leading  to  the  hot-water  fau- 
cets leave  the 
tank  near  the 
top? 

The     name 
"  boiler  "  is  a 


FIG.  51.  A  hot-water  tank. 


wrong    name, 
since  the 

water  should  never  boil  in  the  hot-water 
tank.  In  case  it  should  become  heated  to 
the  boiling  point  it  may  be  cooled  by  allow- 
ing more  cold  water  to  enter  the  tank.  This 
result  may  be  accomplished  by  drawing  off 
some  of  the  heated  water  from  the  faucet 
usually  provided  near  the  bottom  of  the 
tank. 

Waste  pipes  of  the  house.     Quite  as  im- 
portant as  a  supply  of  pure  water  is  the  removal  of  waste  from 


FIG.  52.  A  kerosene  water- 
heater. 

(Courtesy,  Cleveland  Metal 
Products  Company.) 


88  WATER  AND  HOW  WE  USE  IT 

a  house.  Sewage  is  removed  by  a  system  of  pipes  which  start 
from  the  sinks,  bowls,  tubs,  and  water-closets  and  end  in  the 
city  sewer  or  in  a  cesspool  or  septic  tank.  The  principal  pipe 
usually  passes  vertically  through  the  house.  It  is  called  the 
soil  pipe.  Other  smaller  pipes  connect  all  the  sinks,  bowls,  etc., 
with  it.  The  waste  flows  down  the  pipes  by  the  force  of  gravity. 

To  prevent  the  escape  of  sewer  gas  into  the  house,  each  bowl 
has  a  trap  below  it.  A  trap  is  a  water  seal.  Several  types  of  traps 
are  in  common  use.  They  nearly  all  depend  on  the  principles 
that  the  level  of  water  in  connecting  pipes  is  the  same,  and  that 
gases  will  not  force  their  way  down  into  water.  Study  the 
traps  in  your  own  house. 

Sewage  disposal.  The  usual  method  of  sewage  disposal  is  to 
allow  it  to  be  acted  on  by  nature's  scavengers,  the  bacteria  of 
decay.  Unlike  the  bacteria  which  produce  such  diseases  as  ty- 
phoid fever,  these  little  plants  are  constantly  helping  mankind 
by  breaking  down  and  crumbling  all  kinds  of  dead  matter  so  that 
it  can  be  washed  into  the  soil.  There  another  group,  the  soil 
bacteria,  are  waiting  to  attack  it. 

Several  devices  are  in  use  to  enable  the  bacteria  to  come  in 
contact  with  the  sewage.  The  old-fashioned  cesspool,  a  pit  dug 
in  the  ground,  covered  over  with  boards  and  soil,  is  a  crude 
method.  If  the  soil  is  porous,  and  if  the  cesspool  is  located  where 
the  drinking-water  cannot  be  contaminated,  a  cesspool  is  a  fairly 
satisfactory  arrangement  for  a  farmhouse  or  a  house  in  a  small 
village. 

A  better  device  is  a  septic  tank.  It  consists  of  two  or  three  com- 
partments cemented  so  as  to  be  water-tight.  In  the  first  com- 
partment the  sewage  from  the  house  is  acted  on  by  the  bacteria 
of  decay.  Solid  matter  soon  becomes  liquid.  The  liquid  passes 
into  the  second  compartment.  When  this  is  full,  it  empties  into 
drains  under  the  surface  of  the  ground.  They  allow  the  sewage 
to  enter  the  ground,  where  it  is  attacked  by  the  soil  bacteria. 

When  a  large  amount  of  sewage  must  be  disposed  of,  contact 
filter  beds  are  sometimes  used.  They  are  beds  of  broken  stone, 
sand,  or  gravel.  The  sewage  running  through  the  sand  or  gravel 
is  attacked  by  bacteria  and  changed  to  water  and  harmless  gases. 


WATER  IN  OUR  HOUSES  89 

Cities  which  are  near  the  ocean  often  have  their  sewage  car- 
ried through  pipes  ten  or  twenty  miles  out  to  sea. 

Water  changes  from  one  form  to  another:  the  physical  states. 
Water  is  one  of  the  best  substances  to  show  the  three  forms  in 
which  matter  may  exist.  We  all  know  that  water  freezes  to  ice, 
which  is  a  solid  substance;  that  its  usual  state  is  a  liquid;  and 
that  it  may  change  into  water  vapor,  which  is  a  gas.  Every  sub- 
stance that  you  can  think  of  is  in  one  of  these  three  states. 

Water  freezes  to  ice.  Did  you  ever  let  a  bottle  of  water  freeze? 
What  happened  to  the  bottle?  One  peculiar  thing  about  ice  is 
that  it  takes  up  more  space  than  the  water  from  which  it  came. 
It  is  very  fortunate  that  this  is  so.  Since  water  expands  in  chang- 
ing to  ice,  a  certain  volume  of  ice  —  for  example,  a  quart  —  is 
lighter  than  the  same  volume  of  water.  Ice  therefore  rises  to  the 
top  of  water.  If  it  sank  instead  of  rising,  the  ponds  and  rivers 
would  be  solid  ice  in  the  .winter,  and  many  fish  and  water  plants 
would  die. 

The  reason  that  ice  takes  up  more  space  than  water  is  thought 
to  be  due  to  the  way  in  which  the  particles  are  arranged.  Jce  is 
made  of  crystals,  as  you  can  see  by  examining  the  frost  on  a  win- 
dow pane.  The  particles  of  a  crystal  are  arranged  in  beautiful 
patterns,  and  of  course  take  up  more  space  than  if  they  were 
lying  side  by  side. 

The  temperature  at  which  water  freezes  is  perfectly  definite, 
so  that  thermometers  are  marked  by  it.  The  freezing  point  on 
the  Centigrade  thermometer  is  o  degrees;  on  the  Fahrenheit 
thermometer,  32  degrees.  (See  -page  107.)  If  you  should  start 
with  some  warm  water  and  gradually  cool  it,  you  would  find  that 
the  mercury  would  fall  until  the  water  began  to  freeze;  it  would 
then  stay  at  the  freezing  point  until  all  the  water  was  frozen, 
when  it  would  begin  to  fall  again.  The  temperature  at  which 
water  changes  to  ice  is  the  same  as  that  at  which  ice  changes  to 
water;  it  may  be  called  either  the  freezing  point  or  the  melting 
point.  Which  of  the  following  temperatures  are  below  freezing: 
3°  C,  10°  F.,  17°  C,  39°  F.,  6°  C.,  21°  F.? 

Great  care  must  be  taken  in  the  winter  that  the  water  does  not 
freeze  in  the  pipes.  Many  fatal  explosions  have  occurred  when 


90  WATER  AND  HOW  WE  USE  IT 

people  have  started  fires  in  stoves  after  very  cold  nights.  When 
the  water  is  heated,  it  expands.  If  the  pipes  connected  with  the 
hot-water  tank  are  filled  with  ice,  there  is  no  chance  for  the  ex- 
panding water  to  move,  so  it  bursts  the  water-back  of  the  stove. 
A  wise  precaution  is  to  turn  off  the  water  on  very  cold  nights. 

Water  changes  to  vapor.  Even  when  the  temperature  is  not 
high  enough  to  cause  it  to  boil,  the  water  changes  to  vapor,  but 
not  rapidly.  You  can  think  of  many  cases  of  evaporation.  At 
least  once  a  week  it  is  a  matter  of  interest  in  your  home  whether 
the  day  is  a  "good  drying  day."  You  know  some  causes  for 
quick  evaporation ;  you  know  that  clothes  will  usually  dry  more 
quickly  on  a  warm  day  than  on  a  cool  day,  on  a  windy  day  than 
on  a  still  day,  in  dry  air  than  in  moist  air. 

If  you  moisten  your  finger  and  hold  it  in  the  air,  you  feel  that 
it  is  cooler.  This  is  because  when  water  evaporates  some  heat 
is  used  in  changing  it  to  vapor,  and  the  heat  is  taken  from  what- 
ever the  water  is  touching.  If  the  water  is  on  your  finger,  heat  is 
taken  from  your  skin.  Can  you  understand  now  why  you  feel 
chilly. if  you  sit  in  a  draft  with  wet  clothing? 

The  cooling  effect  of  evaporation  is  useful  in  keeping  food.  The 
iceless  refrigerator  depends  in  part  upon  this  principle.  If  a  bottle 
of  milk  is  set  in  a  pan  of  cold  water  and  a  cloth  is  wrapped  around 
the  bottle  so  that  the  cloth  soaks  up  the  water,  the  milk  may  be 
kept  cool  as  long  as  evaporation  is  going  on.  Setting  the  pan 
where  a  breeze  may  blow  over  it  helps  the  water  to  evaporate 
more  quickly. 

Water  changes  to  steam.  If  you  should  start  with  cold  water, 
and  gradually  heat  it,  you  would  find  that  the  temperature  would 
rise  until  the  water  began  to  boil.  There  it  would  stay  until  the 
water  was  boiled  away.  The  boiling  point  is  as  definite  as  the 
freezing  point.  At  sea  level  it  is  100  degrees  on  a  Centigrade 
scale,  and  212  degrees  on  a  Fahrenheit  scale.  The  temperature 
of  steam  is  the  same  as  that  of  the  boiling  water.  Steam  is  water 
vapor  at  the  boiling  point. 

Cooking  food  by  boiling.  The  Italian  soldiers  in  the  Great 
War  who  were  stationed  in  some  of  the  high  passes  in  the  Alps 
found  it  very  hard  to  cook  their  food.  The  reason  is  easy  to  see. 


WATER  IN  OUR  HOUSES  91 

Distance  above  the  sea  level  makes  a  difference  in  the  air-pressure. 
(See  page  9.)  You  have  noticed  in  boiling  water  that  a  bubble 
of  steam  is  first  formed  near  the  bottom  of  the  dish,  where  it  is 
hottest;  the  bubble  then  rises  through  the  water  to  the  surface, 
where  it  bursts  and  the  steam  escapes  into  the  air.  The  air  presses 
down  on  the  surface  of  the  water;  the  greater  the  pressure,  the 
harder  it  is  for  the  steam  bubble  to  burst  and  escape.  Therefore 
we  find  that  as  the  air-pressure  becomes  less,  the  boiling  point 
becomes  lower.  On  the  top  of  Mont  Blanc  the  boiling  point  of 
water  is  only  84  degrees  Centigrade.  When  we  cook  food  by  boil- 
ing, it  is  the  heat  that  really  cooks  it.  If  we  cannot  get  water 
hotter  than  84  degrees,  we  cannot  boil  eggs  or  other  food  as 
quickly  as  we  can  with  water  at  100  degrees. 

On  the  other  hand,  if  the  air-pressure  above  the  water  is 
increased,  the  water  boils  at  a  higher  temperature  than  usual. 
Steam-pressure  canning  outfits  depend  upon  this  principle. 
Keeping  a  tightly  fitting  cover  over  a  dish  in  which  anything  is 
boiling  helps  the  food  to  cook  faster  because  the  boiling  point  is 
raised. 

Changes  produced  in  food  by  boiling.  Boiling  is  only  one 
method  of  cooking  food.  Whatever  method  is  used,  remember 
that  the  heat  really  cooks  the  food.  Water  is  used  as  a  safe  way 
of  applying  the  heat,  and  to  dissolve  certain  parts  of  the  food. 

When  eggs  are  boiled,  the  egg-white  begins  to  change  long  be- 
fore the  water  boils.  Such  a  hardening  as  takes  place  in  the  white 
or  albumen  of  the  egg  is  called  coagulation,  or  clotting.  Since  the 
egg  is  enclosed  in  its  shell,  none  of  its  goodness  is  lost  by  being  dis- 
solved in  the  water.  The  best  way  to  produce  a  tender,  jelly- 
like  egg  is  to  cook  it  for  about  ten  minutes  just  below  the  boiling 
point  of  water.  A  "  dropped  egg  "  must  be  dropped  into  boiling 
water  in  order  to  harden  the  white  quickly,  before  the  water  has  a 
chance  to  dissolve  any  of  its  goodness. 

Two  changes  take  place  in  meat  when  it  is  boiled :  the  fiber  is 
softened  and  the  juices  are  removed.  If  you  wish  to  use  the 
water  in  which  the  meat  is  cooked,  as  in  soup  or  stew,  place  the 
meat  in  cold  water  and  gradually  raise  it  to  the  boiling  point.  In 
this  way  the  juices  are  slowly  removed  from  the  meat  and  dis- 


92  WATER  AND  HOW  WE  USE  IT 

solved  in  the  water.  But  if  you  wish  to  keep  the  juices  in  the 
meat,  as  in  boiled  corned  beef  or  fowl,  heat  it  quickly  by  plunging 
it  in  boiling  water  or  by  searing  the  surface  with  a  flame.  In  this 
way  the  fibers  on  the  surface  are  hardened,  and  the  meat  albumin 
is  coagulated,  thus  forming  a  coating  which  prevents  the  escape 
of  the  juices. 

In  starchy  foods  two  changes  also  take  place.  The  starch 
grains  are  enclosed  within  the  cell  walls.  The  heat  of  the  boiling 
water  causes  the  starch  grains  to  expand  so  much  that  they  burst, 
completely  filling  the  cells,  and  sometimes  breaking  the  cell  walls. 


FIG.  53.  Changes  of  starch  cells  in  cooking:  a,  cells  of  a  raw  potato  with  starch  grains 
in  natural  condition;  b,  cells  of  a  partially  cooked  potato;  c,  cells  of  a  thoroughly  boiled 
potato. 

"  Mealiness  "  is  produced  in  a  potato  by  the  escape  of  some  of 
the  starch  grains  from  the  cells.  Some  of  the  water  in  starchy 
vegetables  also  changes  to  steam.  Unless  this  is  allowed  to  escape, 
it  condenses  again  and  produces  a  "  soggy,"  unattractive  dish. 
Boiling  with  a  large  amount  of  water  is  a  wasteful  way  of  cooking 
vegetables,  because  much  of  the  valuable  food  material  is  dis- 
solved in  the  water.  A  better  way  is  to  use  so  little  water  that  it 
is  almost  boiled  away,  what  is  left  being  served  with  the  vegetable. 
In  this  way  none  of  the  goodness  is  lost. 

Water  as  a  solvent.  We  have  seen  that  water  is  useful  to  us  in 
dissolving  parts  of  our  food,  so  that  it  can  be  readily  digested. 
Water  has  been  called  the  "  universal  solvent  "  because  it  will  dis- 
solve so  many  things.  Will  it  really  dissolve  everything?  Name 
some  substances  that  you  have  been  unable  to  dissolve  in  water. 


WATER  IN  OUR  HOUSES 


93 


Nearly  as  important  to  us  as  its  dissolving  power  on  food  is  the 
dissolving  power  of  water  on  dirt.  We  depend  on  this  power  to 
keep  ourselves  and  our  houses  clean  and  healthful.  While  water 
alone  is  a  good  solvent,  its  dissolving  power  is  increased  by  adding 
other  things  to  it.  What  substances  are  used  in  your  house  to 
help  water  dissolve  dirt? 

Hard  and  soft  water.  Some  water  is  called  "hard,"  some  "  soft." 
The  difference  depends  upon  the  substances  dissolved  in  the  water. 
Hard  water  has  minerals  dissolved  in  it  which  prevent  soap  from 
forming  a  lather.  Hard  waters  are  of  two  kinds,  permanent  and 
temporary.  Water  that  is  not  softened  by  boiling  is  permanent 
hard  water.  Temporary  hard  water  is  softened  by  boiling. 

INDIVIDUAL  PROJECTS 

Working  projects: 

1.  Make  an  iceless  refrigerator. 

For  directions  obtain  the  government  pamph- 
let listed  below. 

2.  Clean  the  traps  in  your  house. 

Consult  your  father  or  the  plumber  as  to  the 
best  way. 

3.  Stop  the  leak  in  a  faucet. 

A  leaking  faucet  usually  shows  the  need  of  a 
new  washer.  The  water  must  be  turned  off  and 
a  wrench  used  to  unscrew  the  faucet.  (See  the 
diagrams  on  page  73.) 


Reports: 

1.  How  the  Panama  Canal  Zone  was  furnished  with 
pure  water. 

A  helpful  book  is  Community  Hygiene,  by 
Woods  Hutchinson. 

2.  How  an  army  obtains  pure  water. 

Read  the  work  of  the  American  army  engineers 
in  France,  and  tell  the  story  of  their  work  to  the 
class. 

3.  Dangers  in  impure  water. 

Write  a  letter  to  a  girl  in  China.  Explain  to 
her  what  the  dangers  are  in  water  which  looks 
clean.  Pure  Water,  by  G.  C.  Whipple,  will  help 
you.  Read  your  letter  to  the  class. 

4.  What  our  State  is  doing  to  stamp  out  typhoid 
fever. 

Write  a  letter  to  the  Department  of  Public  Health  in  your  State  asking 
them  to  send  you  anything  they  can  about  your  project.  Then  study  what 
they  send  you,  and  tell  the  class  about  it. 

5.  How  the  water  for  our  town  is  purified. 

Two  pupils  may  work  on  this  project.     Visit  the  water  department. 


FIG.  54.  An  iceless  refrig- 
erator. It  consists  of  & 
wooden  framework  covered 
with  canton  flannel.  Wicks 
of  the  same  material  rest  in 
a  pan  of  water  on  top.  The 
bottom  pan  also  contains 
water.  From  the  wet  cloth 
the  water  evaporates,  tak- 
ing heat  from  the  inside.  The 
refrigerator  should  stand  in 
a  shady  place  where  air  can 
circulate  freely. 


94  WATER  AND  HOW  WE  USE  IT 

Find  out  all  you  can.     Get  maps  and  photographs  if  possible  to  make  your 
report  to  the  class  as  interesting  as  possible. 

6.  The  water-supply  system  of  our  town. 

If  the  class  is  unable  to  take  the  trip,  two  pupils  may  follow  the  sug- 
gestions given  in  problem  I,  and  report  to  the  class.  If  a  map  cannot  be 
obtained,  drawings  or  diagrams  may  be  put  on  the  board. 

7.  A  water-supply  system  for  a  farmhouse. 

The  best  person  to  report  on  this  project  is  a  boy  who  has  such  a  sys- 
tem in  his  own  house. 

8.  The  hot-water  supply  for  an  apartment  house. 

A  project  for  city  boys  or  girls.  Consult  the  janitor,  make  diagrams, 
and  explain  the  system  to  your  classmates. 

9.  A  gas  water-heater  —  how  it  works. 

If  you  have  a  gas  heater  at  home,  study  it  carefully.  Get  pamphlets 
with  diagrams  from  plumbing-supply  houses.  A  large  diagram  may  be 
drawn  on  the  board  from  which  to  make  your  explanation. 

10.  An  electric  water-heater  —  how  it  works. 

See  suggestions  for  project  9. 

11.  Water  meters  and  how  to  read  them. 

Perhaps  the  water  department  will  lend  you  a  model  of  a  meter.  If 
there  is  a  meter  in  the  school,  study  it  and  show  it  to  the  class.  By  copy- 
ing the  dial  on  the  board  good  practice  in  reading  the  meter  may  be  given 
to  all  the  pupils. 

12.  Traps  in  a  plumbing  system. 

Get  from  a  plumber  as  many  different  kinds  of  traps  as  possible. 
From  questioning  him  and  studying  such  a  book  as  Butler's  Household 
Physics,  explain  to  the  class  how  they  work. 

13.  How  our  town  disposes  of  its  sewage. 

Find  out  from  the  town  authorities  what  becomes  of  the  sewage,  what 
the  sewerage  system  is,  and  what  use,  if  any,  is  made  of  the  waste. 

14.  Sewage  farms. 

If  there  is  a  sewage  farm  in  your  locality,  visit  it  and  report  how  sewage 
is  made  useful. 

15.  The  advantages  of  different  ways  of  cooking. 

If  you  have  had  a  course  in  household  science  or  in  cookery,  write  a 
letter  to  your  mother,  telling  her  all  the  ways  of  cooking  that  you  know, 
and  the  advantages  of  each.  If  you  have  had  no  such  course,  consult  your 
mother  and  such  books  as  Foods  and  Household  Management,  by  Kinne  and 
Cooley,  and  explain  your  project  to  the  boys  in  the  class. 

1 6.  Cleaning  materials  and  their  uses. 

A  good  account  is  given  in  Foods  and  Household  Management. 


BOOKS  THAT  WILL  HELP  YOU 

The  Book  of  Wonders.     Presbrey  Syndicate.     New  York. 

The  story  in  a  glass  of  water,  illustrated. 

Farm  Water  Supplies.    S.  P.  Gates.     Mass.  State  Board  of  Agriculture,  Circu- 
lar 1 8. 

Describes  advantages  of  different  kinds  of  wells. 
Household  Physics.     A.  M.  Butler.     Whitcomb  &  Barrows. 
Physics  of  the  Household.     C.  J.  Lynde.     The  Macmillan  Co. 
Pure  Water:    G.  C.  Whipple.     State  Board  of  Health,  Jacksonville,  Florida. 

Gives  a  good  idea  of  the  dangers  of  an  impure  water-supply,  and  what  a 
city  supply  should  be. 


WATER  IN  OUR  HOUSES  95 

The  Sanitary  Side  of  Farm  Water  Supplies.     X.  H.  Goodnough.     Mass.  State 
Board  of  Agriculture. 

The  Thermometer  and  its  Family  Tree.     P.  R.  Jameson.     Taylor  Instrument 
Companies.     Rochester,  New  York. 

Thermometers  from  the  time  of  their  invention  to  the  present  day,  illus- 
trated. 

"A  Hot-Water  System."    P.  E.  Rowell.    General  Science  Quarterly,  May,  1918. 

How  to  Prevent  Typhoid  Fever.     Farmers'  Bulletin  478.     U.S.  Department  of 
Agriculture. 

An  Iceless  Refrigerator.    Food  Thrift  Series,  no.  4.    U.S  Dept.  of  Agriculture. 


PROJECT  VI    t 
WATER  IN  THE  AIR 

The  weather.  What  is  the  weather  to-day?  If  clouds,  mist, 
rain,  hail,  or  snow  can  be  seen,  they  are  the  result  of  water  in  the 
air.  If  the  day  is  fair,  less  water  is  present,  but  even  on  the  fair- 
est day  the  air  contains  some  water  in  the  form  of  invisible  vapor. 

If  you  could  be  perched  high  above  the  North  Pole,  and  could 
view  the  whole  northern  hemisphere,  you  would  see  a  procession 
of  storms  and  fair  weather  marching  around  the  earth  in  one  di- 
rection, for  weather  is  not  governed  by  chance,  but  by  law. 

The  problems  which  follow  will  show  you  some  of  the  laws 
which  govern  the  weather.  By  solving  them  you  may  become 
partly  independent  of  the  weather  forecasts  in  the  daily  papers. 
You  may  keep  a  scientific  record  of  the  weather  in  two  ways, 
as  directed  in  problems  I  and  9.  By  solving  problems  2-7,  in- 
clusive, you  can  learn  the  causes  of  the  wind,  the  rain,  and  the 
dew.  You  can  learn  how  to  foretell  the  weather  from  a  study  of 
a  weather  map  and  from  noting  the  course  of  storms  (problems 
8,  10,  n).  If  you  live  in  a  city  or  town  where  there  is  a  station 
of  the  United  States  Weather  Bureau,  a  visit  to  the  office  will 
be  enlightening  and  intensely  interesting  (problem  12).  If  you 
live  in  the  country,  it  is  likely  that  some  one  in  your  vicinity  is  a 
volunteer  observer.  Visit  him  and  watch  him  make  his  observa- 
tions. You  may  become  a  volunteer  observer  yourself.  If  you 
wish  to  cooperate  with  the  Government  in  this  way,  write  to  the 
Weather  Bureau,  United  States  Department  of  Agriculture,  for 
Instructions  for  Cooperative  Observers. 

You  may  win  Camp-Fire  honors  by  solving  some  of  these  prob- 
lems, and  advance  in  knowledge  of  Scoutcraft.  You  will  certainly 
obtain  from  this  project  an  intelligent,  scientific  knowledge  of 
the  topic  of  conversation  most  common  to  human  beings,  the 
weather. 


WATER  IN  THE  AIR 


97 


PROBLEM  i :  To  KEEP  A  WEATHER  RECORD. 

Directions  : 

Make  a  table  for  your  weather  observations,  using  the  following  plan. 


DATE 

HOUR 

TEMPERATURE 

CHARACTER  OF 
DAY 

WIND 

REMARKS 

• 

Date.  The  record  should  be  kept  regularly,  without  omission  of  days. 
Camp-Fire  Girls  may  win  an  honor  by  keeping  a  scientific  record  for  a 
month. 

Hour.  The  observations  should  be  made  at  the  same  hour  each  day. 
Temperature.  If  you  have  no  thermometer,  use  the  following  words  to 
describe  the  temperature: 

Very  warm. 
Warm. 
Moderate. 
Cool. 
Cold. 
Very  cold. 

Character  of  Day.  Use  circles  similar  to  those  on  a  weather  map. 
O  Clear. 
O  Partly  cloudy. 
<§  Cloudy. 
©  Rain. 
©  Snow. 

Wind.  Use  arrows  flying  with  the  wind,  as  on  the  weather  map,  calling 
the  top  of  the  page  north. 

Record  also  the  velocity  of  the  wind,  using  the  following  terms: 
Light,  when  just  moving  the  leaves  of  trees. 
Moderate,  when  just  moving  twigs. 
Brisk,  when  moving  large  branches. 
High,  when  blowing  dust  and  papers. 
Gale,  when  breaking  small  branches  from  trees. 

Remarks.  In  this  column  record  any  interesting  features  not  noted  in 
any  other  column,  such  as  killing  frosts,  thunderstorms,  hail,  sleet,  auroras, 
unusual  coloring  of  sky. 


98 


WATER  AND  HOW  WE  USE  IT 


Summary: 

1.  What  was  the  highest  temperature  noted?  the  lowest?  the  range  of 
temperature? 

2.  How  many  days  were  clear?  cloudy?  rainy?  snowy? 

3.  Does  the  wind  seem  to  blow  from  any  special  direction  during  a  storm? 
If  so,  from  what  direction? 

4.  Does  the  wind  blow  from  any  special  direction  after  a  storm?     If  so, 
from  what  direction? 

5.  Is  the  temperature  warmer  before  or  after  a  storm? 

6.  What  is  the  relation  between  the  wind  direction  and  the  tempera- 
ture? 


PROBLEM  2:  How  DOES  WATER  VAPOR  GET  INTO  THE  AIR? 

Directions: 

Part  i.  Does  the  air  contain  water? 

Set  a  glass  of  ice  water  on  the  table.     What  appears  on  the  outside  of 
the  glass?   From  where  did  it  come?  Why  could  you  not  see  it  before? 

Part  2.  What  are  the  sources  of  water  vapor? 

Pour  a  measured  amount  of  water  into  a  shal- 
low dish,  and  set  it  in  a  warm  place,  in  the  sun 
if  possible.  Measure  it  again  the  next  day.  Is 
the  amount  the  same?  Why? 

Arrange  an  apparatus  like  the  diagram.  The 
stem  of  the  leaf  is  in  the  water  in  the  lower  glass. 
The  hole  in  the  cardboard  must  be  only  large 
enough  to  allow  the  stem  to  pass  through.  The 
upper  glass  must  be  perfectly  dry.  Set  the  ap- 
paratus in  the  sun.  What  appears  on  the  upper 
glass?  From  where  did  it  come? 

\  /  Conclusion: 

\  I  What  are  two  sources  of  water  vapor  in  the 

V. /  air? 


FIG.  55.  An  apparatus  to 
show  one  way  in  which 
water  gets  into  the  air. 


Question: 

What  example  can  you  name  of  water  enter- 
ing the  air  in  each  of  the  ways  suggested  above? 


PROBLEM  3:  How  is  AIR  AFFECTED  BY  A  CHANGE  OF  TEMPERATURE? 

Directions: 

Draw  a  piece  of  glass  tubing  to  a  point.  Insert  the  tubing  through  the 
hole  in  a  one-holed  rubber  stopper  which  fits  closely  into  the  neck  of  a  thin- 
walled  glass  flask.  Pour  water  into  a  glass  until  it  is  about  two- thirds  full 


WATER  IN  THE  AIR 


99 


Add  a  few  drops  of  red  ink  to  the'water.     Support  the  flask  over  the  glass 
with  the  large  end  of  the  tube  in  the  water. 

Heat  the  flask  gently  with  the  hands.     What  happens?    Why? 

Remove  the  hands.     Explain  what  happens.     Heat  the  flask  carefully 
with  a  flame.    Explain  the  results.    Heat 
as  long  as  results  may  be  seen. 

What  happens  when  the  flame  is  re- 
moved? Why? 

Conclusions: 

1.  What  are  the  results  of  heating  air? 

2.  What  are  the  results  of  cooling  air? 

PROBLEM  4 :  How  is  TEMPERATURE 

MEASURED? 

Directions: 

Part  i.  Study  of  a  Fahrenheit  ther- 
mometer. 

Examine  the  thermometer  used  in  the 
schoolroom.  Why  is  it  used?  What  are 
its  parts?  What  is  the  liquid  in  the  tube? 

Hold  your  fingers  on  the  bulb.  What 
is  the  effect?  Why? 

Breathe  on  the  bulb.     What  is  the  effect? 

Hold  a  cloth  wet  with  cold  water  on  the  bulb.     What  is  the  effect? 

Part  2.  Comparison  of  two  thermometer  scales. 

Examine  a  thermometer  used  in  scientific  work.  If  it  is  marked  off  with 
both  the  Fahrenheit  and  Centigrade  scales,  compare  the  two  ways  of 
dividing. 

What  is  the  temperature  of  the  room  according  to  the  Fahrenheit  scale? 
according  to  the  Centigrade  scale? 

Is  the  Centigrade  degree  larger  or  smaller  than  the  Fahrenheit 
degree? 

Put  the  thermometer  in  a  dish  of  water.  Heat  the  water  until  it  boils. 
What  is  the  boiling  point  on  the  Fahrenheit  scale?  on  the  Centigrade 
scale? 

If  you  can  get  some  snow  or  chipped  ice,  put  the  thermometer  in  it. 
W7hat  are  the  freezing  points  on  the  two  scales? 

Summary: 

1.  What  is  the  principle  on  which  the  thermometer  depends? 

2.  How  many  degrees  are  there  between  the  freezing  point  and  the 
boiling  point  on  each  scale? 

3.  How  many  Fahrenheit  degrees  are  equal  to  one  Centigrade  degree? 


FIG.  56.  The  effect  of  heating  air. 


ioo  WATER  AND  HOW  WE  USE  IT 

PROBLEM  5:  WHAT  is  ONE  OF  THE  CAUSES  OF  THE  WIND? 

Directions: 

Take  a  shoe  box  or  any  wooden  box  and  cut  two  holes  in  the  top.  Place 
chimneys  over  these  openings.  Burn  a  candle  as  shown  in  the  diagram. 
When  the  candle  is  burning  and  the  chimneys  are  in  place,  hold  some 
burning  joss  sticks  above  the  chimney  under  which  no  candle  is  burning. 
Trace  the  current  of  air.  Explain. 

Question: 
Why  may  a  current  of  air  usually  be  felt  near  a  large  fire? 

PROBLEM  6:  WHAT  MAKES  THE  RAIN? 

Directions: 

Support  a  large  glass  beaker,  about  one  third  full  of  water,  over  a  flame. 
Cover  the  beaker  with  a  clean  aluminum  cover. 

Heat  the  water  carefully.  Observe  everything  that  happens.  Give 
reasons  for  every  change  that  takes  place. 

Conclusions: 
Basing  your  answer  upon  this  experiment,  explain  how  rain  is  formed. 

Question : 

In  what  ways  are  the  conditions  in  this  experiment  unlike  those  of 
nature? 

PROBLEM  7:  How  DOES  EXPANSION  AFFECT  THE  TEMPERATURE  OF  A  GAS? 

Directions: 

Allow  a  little  compressed  gas  to  escape  from  its  container.  (The  com- 
pressed air  used  for  filling  tires  in  a  garage  may  be  used.  A  jar  of  nitrous 
oxide,  such  as  is  used  by  dentists,  is  excellent.)  How  does  the  tempera- 
ture of  the  expanding  gas  compare  with  the  temperature  of  the  air 
around  it? 

Hold  a  thermometer  near  the  opening.    How  is  it  affected? 

Conclusion: 

When  air  expands,  how  is  its  temperature  changed? 

Question: 

Can  you  explain  why  raindrops  form  in  expanding  air? 

PROBLEM  8 :  WHAT  MAKES  THE  DEW? 

Directions: 

Put  some  water  into  a  glass  or  calorimeter,  the  outer  surface  of  which  is 
polished.  Add  pieces  of  chipped  ice  and  note  carefully  any  difference  in 
the  appearance  of  the  outside  of  the  container. 


WATER  IN  THIS  AIR 


101 


Summary:  '*,*/•'  ?a   *•*  *   >-/ 

What  is  the  origin  of  the  drops  of  moisture?    Explain  how  this  experi- 
ment illustrates  how  dew  is  formed. 

Questions: 

1.  Does  the  dew  "fall"? 

2.  Why  do  cold-water  pipes  "sweat"  in  the  summer? 

3.  Why  does  a  mist  sometimes  form  upon  a  person's  eyeglasses  when  he 
comes  into  a  warm  room  from  a  colder  place? 

4.  Why  is  it  possible  to  "see  your  breath"  in  winter? 

PROBLEM  9:  To  UNDERSTAND  A  WEATHER  MAP. 

Directions: 

(Note  —  Each  pupil  should  be  provided  with  a  weather  map.) 

In  what  city  was  your  map  made? 
On  what  day  was  your  map  made? 
At  what  time  of  day  were  the  observations  taken? 
By  what  Government  department  was  the  map  made? 
Find  the  continuous  black  lines.     What  numbers  are  at  the  end  of  the 
lines?     What  do  they  mean?    Why  are  the  lines  not  straight? 

Find  the  dotted  black  lines.    What  numbers  are  at  the  ends?    What  do 
they  mean? 

Find  the  small  circles.   How  do  they  differ?    What  do  the  shading  and 
letters  mean? 

Find  the  arrows  attached  to  the  circles.     Do  they  all  point  in  the  same 
direction?    What  do  they  mean? 
What  do  the  shaded  a'reas  show? 

With  what  lines  are  the  words  HIGH  and  LOW  connected?    To  what  do 
they  refer? 

Do  the  arrows  show  that  the  wind  usually  blows  toward  or  away  from 
a  LOW?  a  HIGH? 

What  facts  are  given  in  the  columns  in  the  lower  corner  that  are  not 
given  on  the  map? 

Find  on  the  map  the  places  that  had 
The  highest  temperature. 
The  lowest  temperature. 
The  greatest  air-pressure. 
The  least  air-pressure. 
Find  in  the  columns  the  places  that  had 

The  highest  temperature  by  day. 
The  lowest  temperature  by  night. 
The  greatest  change  between  day  and  night. 
The  highest  wind  velocity. 
The  greatest  rainfall  (precipitation). 
In  each  case  give  the  name  of  the  place  and  the  exact  figures. 


102 


WATER  AND  HOW  WE  USE  IT 


Summary:       \':  \  *  \   *  "\\  ^,  *  ' *\ 

You  should  now  be  able  to  tell,  by  a  glance  at  the  weather  map,  — 

1.  What  part  of  the  country  was  having  a  storm. 

2.  Where  the  weather  was  fair. 

3.  The  direction  of  the  storm  center  from  your  own  city. 

4.  The  weather  of  any  given  place  on  the  day  the  map  was  made. 


FlG.  57.  A  weather  map  for  8  A.M.,  December  30, 1907,  showing  a  typical  cyclonic 
storm,  and  the  path  over  which  its  center  has  passed. 

EXPLANATORY  NOTES 

Observations  taken  at  8  A.M.,  75th  meridian  time. 

Air  pressure  reduced  to  sea  level. 

ISOBARS  (continuous  lines)  pass  through  points  of  equal  air  pressure. 

ISOTHERMS  (dotted  lines)  pass  through  points  of  equal  temperature;  drawn  for 

every  10°. 
SYMBOLS  indicate  state  of  weather:  Q  clear;  3  partly  cloudy;  •  cloudy;  ®  rain; 

©  snow;  0  report  missing. 
Arrows  fly  with  the  wind. 

SHADED  AREA  shows  precipitation  of  o.oi  inch  or  more  during  last  24  hours. 
Wind  velocities  of  less  than  10  miles  an  hour,  and  amounts  of  precipitation  of  less 
than  o.oi  inch,  are  not  published  her  eon. 

PROBLEM  10:  To  KEEP  A  GRAPH  OF  THE  WEATHER. 

Directions: 

You  will  need  a  sheet  of  cross-section  paper.  Mark  off  the  sheet  to 
record  the  date,  the  temperature,  the  air-pressures,  the  wind  direction,  the 
cloudiness,  and  the  presence  of  HIGHS  and  LOWS.  (See  figure  58.) 


WATER  IN  THE  AIR 


103 


Date 


Weather 
and 
Wind 


PROBLEM   n:  To  TRACE  THE 
COURSE  OF  A  STORM. 

Directions: 

Use  a  large  blackboard  wall 
map  of  the  United  States. 
Make  several  paper  circles 
about  eight  inches  in  diameter, 
using  one  color  for  LOWS,  and 
another  color  for  HIGHS. 

On  the  day  when  you  begin 
this  problem,  locate  on  the 
latest  weather  map  the  LOW 
which  is  nearest  to  the  Pacific 
Coast.  Fasten  the  paper  disk 
to  represent  this  LOW  in  place 
on  the  wall  map. 

On  the  next  day  find  the  po- 
sition of  this  LOW,  which  will 
probably  have  moved  toward 
the  east.  Put  another  disk  on 

the  map  to  represent  the  new  position,  and  connect  the  two  disks  with 
arrows  to  show  the  direction  of  movement  of  the  storm.  If  a  HIGH  has 
appeared  near  the  western  coast,  place  a  disk  on  the  wall  map  to  show  its 
position. 

On  the  next  day,  place  disks  to  show  the  new  positions  of  the  LOW 
and  the  HIGH  which  you  are  tracing,  connecting  the  positions  with 
arrows. 

Continue  to  do  this  each  day  until  the  LOW  and  the  HIGH  disappear 
from  the  map. 


Highs- 
Lows 


Jan. 

11  12  13  14  15  16  17  18  19  20  21  22  23  24  25 


From  a  daily  study  of  the  weather  map,  make  the  proper  record  for 
each  day  for  your  own  city. 

Summary: 

1.  What  conditions  of  pres- 
sure, temperature,  and  sky  have 
you  found   connected  with  a 
HIGH? 

2.  What  conditions  have  you 
found  connected  with  a  LOW? 

3.  What   is    the    usual    di- 
rection of  the  wind  when  the 
weather  is  clear?  when  rainy? 
just  before  a  storm? 


Low 


High 


FIG.  58.  A  weather  graph. 


104  WATER  AND  HOW  WE  USE  IT 

Summary: 

1.  What  course  was  followed  by  the  storm? 

2.  What  course  was  followed  by  the  area  of  high  pressure? 

PROBLEM  12:  WHAT  PATHS  DO  STORMS  FOLLOW? 

Directions: 

You  will  need  several  weather  maps  of  consecutive  dates,  and  a  blank 
weather  map,  which  may  be  obtained  from  the  local  Weather  Bureau. 

How  many  LOWS  appear  on  the  map  of  the  first  date?  What  is  the 
nearest  city  to  each  LOW? 

On  a  blank  map  make  a  circle  to  represent  the  LOW  which  is  nearest  the 
Pacific  Coast.  Print  in  the  circle  the  word  LOW  and  the  date. 

Examine  the  map  of  the  next  date.  Are  the  LOWS  located  in  the  same 
places  as  before?  Represent  on  the  blank  map  the  new  position  of  the 
LOW  which  you  noted  above.  (Note:  Storms,  or  LOWS,  generally  move 
across  the  United  States  from  west  to  east.) 

Plot  the  position  of  the  LOW  until  it  disappears  from  the  map. 

Connect  the  circles  with  a  line  of  arrows  to  represent  the  course  of  the 
storm. 

Summary: 

1.  Near  what  large  cities  did  the  storm  pass? 

2.  How  many  days  were  required  for  the  storm  to  cross  the  country? 

3.  From  a  comparison  with  the  paths  observed  by  other  pupils  in  the 
class,  do  you  find  any  regular  paths  followed  by  storms? 

PROBLEM  13:  A  TRIP  TO  THE  LOCAL  WEATHER  BUREAU  TO  LEARN  ITS 
WORK. 

Directions: 

Go  to  the  office  of  the  local  Weather  Bureau,  and  obtain,  if  possible 
from  your  own  observation,  the  following  information: 

1.  How  the  temperature  is  measured. 

2.  How  the  air-pressure  is  measured. 

3.  How  the  direction  of  the  wind  is  found. 

4.  How  the  velocity  of  the  wind  is  found. 

5.  How  the  amount  of  rainfall  is  found. 

6.  How  the  time  of  sunshine  and  shadow  is  recorded. 

7.  How  the  weather  map  is  made. 

8.  How  the  weather  signals  are  displayed. 

Summary: 

Describe  what  you  have  seen  and  learned  of  the  work  of  the  Weather 
Bureau  in  a  letter  to  a  friend. 


WATER  IN  THE  AIR  105 

Water  in  an  invisible  form  in  the  air.  Water  is  always  present 
in  the  air  in  the  form  of  an  invisible  gas  called  water  vapor.  In 
order  to  understand  how  the  air  contains  water  in  a  gaseous  form 
it  is  helpful  to  compare  it  to  a  sponge,  (i)  A  sponge  can  hold 
water.  So  can  the  air  hold  water  in  the  form  of  water  vapor. 
Water  in  a  liquid  form  is  able  to  soak  in  between  the  parts  of  the 
sponge.  In  some  such  way  it  is  possible  for  water  vapor  to  be 
soaked  up  by  the  air.  (2)  The  sponge  can  hold  only  a  limited 
amount  of  water.  That  is  also  true  of  the  air  in  regard  to  water 
vapor.  (3)  When  a  sponge  is  holding  all  the  water  possible  it 
is  said  to  be  saturated.  The  same  expression  is  used  with  refer- 
ence to  the  air  when  it  is  holding  all  the  water  vapor  that  it 
can. 

How  the  water  vapor  gets  into  the  air.  The  air  gets  its  water 
vapor  by  means  of  a  process  called  evaporation.  This  is  the  chang- 
ing of  water  from  a  visible  liquid  into  an  invisible  gas.  The 
rapidity  of  the  process  of  evaporation  depends  upon  four  factors : 
(i)  the  amount  of  water  vapor  already  present  in  the  air;  (2)  the 
temperature;  (3)  the  air-pressure;  (4)  movement  of  the  air. 

If  the  air  is  already  saturated  with  water  vapor,  it  is  impossible 
for  more  vapor  to  enter,  just  as  it  is  impossible  for  a  sponge  to  soak 
up  more  water  when  it  is  saturated.  Dry  air,  on  the  other  hand, 
allows  vapor  to  enter  easily. 

Heat  increases  the  rapidity  of  evaporation.  Especially  when 
the  sun  is  shining,  large  quantities  of  water  are  drawn  off  from  the 
surface  of  the  earth,  particularly  from  the  surfaces  of  rivers,  lakes, 
and  oceans. 

The  third  factor  which  helps  to  determine  the  rapidity  of  evap- 
oration is  the  air-pressure.  There  is  more  rapid  evaporation 
when  the  air-pressure  is  low.  By  using  an  exhaust-pump,  thus 
reducing  the  pressure  of  the  air,  it  is  possible  to  make  water  evap- 
orate so  quickly  that  it  actually  boils  when  cool.  The  commotion 
of  boiling  is  caused  by  the  expansion  or  enlargement  of  particles 
of  the  liquid  into  a  gaseous  form.  This  change  occurs  close  to  the 
applied  heat.  As  water  vapor  occupies  about  sixteen  hundred 
times  the  space  formerly  occupied  by  the  water,  it  is  much  lighter 
and  rises  to  the  surface  in  the  form  of  bubbles.  Upon  the  tops 


io6  WATER  AND  HOW  WE  USE  IT 

of  high  mountains  boiling  is  not  sufficient  to  cook  some  kinds  of 
food.  Why  is  this  so?  (See  page  91.) 

Evaporation  takes  place  more  rapidly  in  moving  air  than  in  still 
air.  After  a  rain  the  streets  dry  quickly  if  the  wind  is  strong. 

Where  the  water  vapor  comes  from.  The  oceans  of  the  world 
are  the  greatest  source  of  the  water  vapor  in  the  air.  Large  inland 
bodies  of  water,  such  as  the  Great  Lakes  and  the  Amazon  River, 
furnish  a  large  amount,  as  do  all  the  smaller  lakes  and  rivers.  The 
surface  of  the  solid  earth  is  also  constantly  losing  water  to  the  air. 
When  winds  blow  from  a  cool  to  a  warmer  region,  they  keep  in- 
creasing their  capacity  to  hold  water,  and  absorb  moisture  from 
anything  they  can.  The  trade  winds,  for  example,  blow  toward 
the  hottest  part  of  the  earth.  They  cause  so  much  water  to  be 
evaporated  from  the  earth  that  many  of  the  regions  over  which 
they  blow  are  deserts. 

Other  sources  of  water  in  the  air  are  the  living  bodies  of 
plants  and  animals. 

Evaporation  from  plants.  Plants  are  constantly  giving  off  water 
by  evaporation.  Some  of  it  is  a  result  of  breathing,  since  water 
is  formed  among  other  substances  when  food  is  oxidized  in  the 
cells. 

By  far  the  largest  amount  of  water  that  is  given  off  by  plants, 
however,  is  transpired.  As  you  know,  plants  absorb  much  water 
from  the  soil  cells,  and  with  it,  mineral  foods  that  the  soil  con- 
tains. When  it  enters  the  roots  of  the  plants,  the  water,  con- 
taining the  mineral  food,  passes  from  cell  to  cell  in  the  plant 
body.  Since  more  water  flows  through  the  plant  than  can  be 
used  to  manufacture  plant  food,  some  of  it  is  evaporated  through 
the  opening  in  the  leaves  to  the  outside  air.  The  amount  that 
may  evaporate  is  very  great  —  a  grass  plant  may  transpire  in  one 
day  more  than  its  weight.  Botanists  have  estimated  that  about 
half  a  ton  of  water  may  evaporate  in  a  day  from  an  ordinary  city 
lot  covered  with  grass.  The  process  by  which  water  passes  out 
of  the  leaves  is  called  transpiration. 

The  thermometer.  In  order  to  measure  the  temperature  of  the 
air  it  is  necessary  to  make  use  of  an  instrument  called  the  ther- 
mometer. 


WATER  IN  THE  AIR 


107 


Melting  point  of  common  solder 


The  first  thermometer  was  made  by  the  great  Italian  scientist,  Galileo. 
It  consisted  of  a  bulb  of  air  connecting  with  a  tube,  the  end  of  which  dipped 
into  a  dish  of  water.  The  water  fell  in  the  tube  as  the  air  expanded  and 
rose  in  the  tube  as  the  air  contracted.  *  e, 

The  instrument  was  not  very  exact, 
however,  because  the  pressure  of  the 
air  affected  it  as  well  as  the  tempera- 
ture. So  a  little  later,  in  1612,  Galileo 
made  a  thermometer  using  a  sealed 
tube  containing  alcohol.  The  tube  was 
marked  off  with  little  enamel  beads. 
Alcohol,  usually  colored  red,  is  still  used 
in  some  thermometers.  The  material 
which  has  proved  the  best  is  the  heavy 
liquid,  mercury,  which  is  also  used  in 
barometers.  (See  p.  5.) 

For  about  one  hundred  years  after 
Galileo  invented  the  thermometer, 
people  were  undecided  how  to  mark 
it  off.  Then,  in  1714,  Fahrenheit  (Far'- 
en-hite)  suggested  a  plan  which  is  still 
used  in  the  English-speaking  countries. 
The  two  fixed  points  are  the  boiling 
point  of  water,  212  degrees,  and  the 
freezing  point  of  water,  32  degrees. 
Zero  was  supposed  then  to  be  the  low- 
est temperature  obtained  by  a  freezing 
mixture. 

The  Centigrade  scale  is  more  con- 
venient for  several  reasons.  The  boil- 
ing point  of  water  is  100  degrees,  and 
the  freezing  point  o  degrees.  This 
scale  is  used  in  France,  and  also  for 
all  scientific  work. 

Since  both  types  of  thermometers 
are  used  in  America,  it  is  well  to  know 
both  scales.  According  to  the  Fahren- 
heit system,  there  are  180  degrees 
between  the  freezing  point  and  the 
boiling  point.  According  to  the  Cen- 
tigrade system  there  are  100  degrees 
between  the  same  two  points.  Therefore,  one  Centigrade  degree  equals 
1.8  Fahrenheit  degrees.  If  the  temperature  of  the  room  is  20  degrees 
Centigrade,  it  is  20  degrees  above  the  freezing  point.  It  is  1.8  times  20 


Botiingpoint  of  water  at  normal  pretture 


Pasteurizing  milk 


Normal  temperature  of  At 


i  body 


cupante  are  not  exercising 


•  Freezing  point  of  water 


•  Fruttnff  point  of  mercury 


FIG.  59.    Two  common  temperature 
scales,  Fahrenheit  and  Centigrade. 

(Courtesy,  U.S.  Bureau  of  Standards.) 


io8 


WATER  AND  HOW  WE  USE  IT 


WATER  BOILS. 


ICC  MELTS. 
SNOW ...  SALT. 
MCRCURT  FREEZES 

LOWEST  NATURAL  TEMP. 
SOLID  C4RBOH  DIOXIDE. 


degrees  or  36  Fahrenheit  degrees  above  the  freezing  point.  Since  the 
freezing  point  in  the  Fahrenheit  scale  is  32  degrees  above  zero,  36  degrees 
above  freezing  equals  68  degrees  above  zero.  A  room  temperature,  then, 
which  registers  20  degrees  on  a  Centigrade  thermometer  registers  68  de- 
grees on  a  Fahrenheit  thermometer. 

Temperature  and  the  amount  of  water  vapor  in  the  air. 
Heat  causes  more  rapid  evaporation  of  water  into  water  vapor. 
Hot  air  can  also  contain  more  water  vapor 
than  cold  air.  In  other  words,  the  higher 
the  temperature  of  the  air,  the  greater  the 
amount  of  water  vapor  it  can  hold. 

Humidity  of  the  air.  The  term  humidity 
refers  to  the  amount  of  water  vapor  in  the 
air.  There  are  two  different  senses  in  which 
the  word  humidity  is  used.  It  may  be  used 
to  refer  to  the  actual  amount  of  water  vapor 
in  the  air.  This  is  known  as  absolute  hu- 
midity. In  a  slightly  different  sense,  this 
term  is  used  to  refer  to  the  comparative 
amount  of  water  vapor  which  the  air  con- 
tains with  that  which  it  would  contain  if 
saturated.  This  is  called  relative  humidity, 
and  it  is  in  this  sense  that  the  word  is  or- 
dinarily used  when  referring  to  the  percent- 
age of  humidity.  If  you  look  under  the 
heading  of  the  weather  report  in  some 
newspapers,  you  will  find  facts  concerning 
the  percentage  of  humidity  in  the  air  dur- 
ing certain  hours  of  the  preceding  day.  For  example,  you  might 
find  that  the  humidity  at  noon  was  fifty  per  cent.  This  would 
mean  that  at  that  time  the  air  was  holding  just  half  of  the  total 
amount  of  water  vapor  that  it  was  capable  of  holding.  As  you 
have  found  in  a  previous  project,  the  amount  of  water  vapor  in 
the  air  is  one  of  the  important  factors  to  be  considered  in 
ventilation.  (See  page  55.)  On  close,  "muggy"  days,  the 
humidity  is  high;  on  days  which  are  invigorating,  the  humidity 
is  low.  There  is  a  great  variation  in  the  percentage  of  humidity 


212° 


32 
0° 

-40' 
-7S' 

-1084 


-297.0. 


-422:7 


'LIQUID  OXYGEN 
^iaUlS  WTROGEW 


UOUID  HYDROGEN. 


O 


FIG.  60.  Some  low  temper- 
atures and  their  effects. 

{Courtesy,  Professor  Louis 
Derr.) 


WATER  IN  THE  AIR  109 

in  different  places  and  in  the  same  place  at  different  times. 
Thus,  in  some  sections  of  the  United  States,  as  along  the  coast 
or  near  great  bodies  of  inland  waters,  the  humidity  is  apt  to  be 
high  most  of  the  time;  whereas  in  places  far  inland  the  humidity 
is  usually  low. 

Condensation.  When  the  temperature  of  the  air  is  lowered, 
the  air  is  able  to  hold  less  water  vapor.  If  the  temperature 
reaches  below  the  point  at  which  the  air  is  saturated,  then 
some  of  the  water  vapor  is  "squeezed  out  "  of  the  air  in  the 
form  of  fine  drops  of  water.  This  change  from  water  vapor  to 
water  is  spoken  of  as  condensation.  Thus  clouds,  mist,  rain,  etc., 
are  all  due  to  the  condensation  to  water  vapor.  This  phenome- 
non usually  occurs  high  in  the  air  because  the  air  is  cooler  there 
than  near  the  surface  of  the  earth  and  so  cannot  hold  so  much 
water  vapor.  One  reason  for  the  upper  air  being  cooler  than  air 
near  the  ground  is  that  as  air  rises,  it  expands.  Expanding  air 
becomes  cooler,  as  you  found  in  problem  7. 

When  condensation  takes  place  close  to  the  ground,  the  drop- 
lets of  water  may  be  deposited  upon  the  grass,  forming  dew. 
When  the  condensation  occurs  near  the  ground  after  the  air  has 
reached  the  saturation  point,  mist  or  fog  is  produced.  When  con- 
densation takes  place  high  in  the  air,  clouds  are  formed,  and  if 
it  is  cold  enough,  the  moisture  is  frozen  into  snow  or  hail.  How 
do  you  explain  the  frost  which  appears  on  windows  in  the 

winter? 

% 

Kinds  of  clouds.  There  are  several  different  kinds  of  clouds.  Nimbus 
is  a  general  term  usually  applied  to  any  cloud  from  which  rain  is  falling. 
Cumulus  is  the  kind  which  appears  before  thunderstorms.  Cirrus  is  a 
fleecy  kind  of  cloud  that  is  very  high,  usually  about  five  miles  above 
ground ;  and  stratus  is  the  kind  which  completely  covers  the  sky  on  rainy 
days.  The  cirrus  clouds  which  are  the  highest  do  not  consist  of  mist,  but 
of  very  small  ice-crystals  because  of  the  great  cold  at  that  height.  The 
so-called  "mackerel  sky,"  the  wind  clouds  of  the  sailors,  is  known  as  the 
cumulo-stratus,  since  it  is  really  composed  of  many  small  cumulus  clouds 
which  stretch  across  the  sky. 

Thunderstorms.  Thunderstorms  almost  always  occur  in  the 
summer  because  at  that  time  conditions  are  favorable  for  them. 


no  WATER  AND  HOW  WE  USE  IT 

The  earth,  heated  by  the  sun's  rays,  warms  the  air  which  is  close 
to  it.  Since  heated  air  is  lighter  than  cool  air,  it  rises,  expands, 
and,  becoming  rapidly  cooled,  causes  the  water  vapor  in  it  to  be 
condensed.  This  usually  results  in  the  formation  of  cumulus 
clouds,  and,  as  already  stated,  masses  of  these  clouds  indicate  the 
likelihood  of  thunderstorms.  The  thunder  and  lightning  which 
accompany  such  storms  are  due  to  the  discharge  of  atmospheric 
electricity.  Hailstorms  are  really  thunderstorms  which  are  pro- 
duced when  there  are  strong  currents  in  the  air.  These  air  cur- 
rents do  not  permit  of  the  immediate  falling  of  the  condensed 
vapor  until  the  droplets  have  been  frozen  into  little  pellets.  These 
in  turn  receive  coatings  of  moisture,  which  freeze  as  they  are 
driven  through  the  cold  upper  regions  of  the  air.  Thus  a  hail- 
stone is  made  up  of  masses  of  ice  frozen  about  a  small  original 
droplet. 

Dew  and  its  formation.  From  what  has  already  been  said, 
perhaps  you  can  explain  how  dew  is  formed.  After  sundown  the 
earth  cools  off  more  rapidly  than  the  air.  Therefore  the  part  of 
the  air  which  is  close  to  the  earth  or  to  objects  upon  the  surface, 
such  as  blades  of  grass,  leaves,  etc.,  is  somewhat  cooler  than  the 
rest  of  the  surrounding  air.  Since  the  air  always  contains  some 
water  vapor  and  since  cool  air  cannot  hold  as  much  of  this  as 
warm  air,  it  becomes  evident  that  if  the  air  is  near  the  satura- 
tion point  a  slight  cooling  may  produce  condensation.  This 
condensation  causes  drops  of  water  to  be  deposited  which  we 
call  dew.  When  the  sun  rises  the  following  morning  and  warms 
the  earth,  this  dew  is  evaporated,  again  becoming  water  vapor. 
The  temperature  at  which  dew  forms  at  any  particular  time  is 
called  the  dew-point. 

The  wind.  You  have  felt  the  force  of  the  wind.  You  know 
that  air  is  a  real  substance.  You  have  noticed  the  dust,  the  bits  of 
paper,  and  the  dead  leaves  which  are  blown  about,  and  you  are 
sure  that  the  wind  is  connected  with  the  movement.  Wind  is  air 
in  motion. 

So  much  is  evident.  But  have  you  ever  considered  what  causes 
the  air  to  move?  It  is  because  of  a  failure  to  balance.  If  two 
open  flasks  of  air  are  exactly  balanced,  and  one  is  heated,  the  bal- 


WATER  IN  THE  AIR  in 

ance  is  disturbed.  »  The  cold  air  is  heavier  than  the  warm  air, 
and  presses  down  with  greater  weight  than  the  warm  air.  If  in- 
stead of  considering  two  volumes  of  air  enclosed  in  flasks  we 
consider  volumes  which  are  free  to  move  in  any  direction,  we  can 
understand  that  if  for  any  reason  one  part  of  the  air  becomes 
lighter,  the  heavier  air  near  it  will  press  down  and  crowd  the 
lighter  air  up.  In  this  way  a  circulation  of  air  is  established. 
The  word  wind  is  used  only  for  the  horizontal  movements  of  the 
air.  The  rising  and  descending  columns  are  called  currents. 

Three  common  causes  for  unequal  pressure  of  air  are  known. 
The  first  and  best-known  is  heat.  You  have  seen  sparks  fly  up- 
ward from  a  bonfire  or  from  a  burning  house.  They  are  borne 
by  the  current  of  moving,  heated  air.  We  say  that  heated  air 
expands.  Equal  volumes  of  cold  air  and  warm  air  do  not  press 
with  equal  weight.  The  heavier  air  presses  in  under  the  lighter, 
warm  air,  which  is  thus  forced  upward.  This  fact  explains  the 
currents  of  cool  air  which  you  feel  blowing  along  the  floor  toward 
the  stove.  It  also  explains  the  sea  breezes  which  spring  up  on 
summer  afternoons  along  the  coast.  Land  absorbs  heat  more 
rapidly  than  water,  therefore  the  air  over  the  land  becomes  heated, 
expands,  and  is  forced  up  by  the  heavier  air  pressing  in  from  over 
the  sea.  The  great  belt  of  heated  air  near  the  equator  is  also 
explained  in  this  way,  since  the  most  direct  and  therefore  the 
hottest  rays  of  the  sun  fall  near  the  equator. 

A  second  cause  of  unequal  pressure  is  the  presence  of  moisture  in 
the  air.  Strange  as  it  may  seem  to  you,  moist  air  is  lighter  than 
dry  air.  This  is  because  a  volume  of  water  vapor  is  lighter  than 
an  equal  volume  of  nitrogen  or  oxygen.  Moisture  in  the  air  takes 
the  place  of  other  gases ;  the  air  therefore  becomes  lighter.  Mois- 
ture-laden air  presses  down  with  less  force  than  dry  air,  as  can 
be  readily  seen  on  a  damp  day  preceding  a  storm,  when  the  ba- 
rometer registers  "  low  "  pressure.  Wherever  the  pressure  is  the 
lowest,  a  current  of  upward-moving  air  is  established  because  the 
heavier,  dryer  air  presses  in  from  every  side. 

A  third  cause  of  unequal  pressure  is  the  presence  of  air  waves. 
Every  aviator  knows  that  there  are  waves  in  the  air,  just  as  there 
are  in  the  sea.  One  reason  for  their  presence  is  the  unevenness  of 
the  surface  of  the  land. 


112 


WATER  AND  HOW  WE  USE  IT 


Imagine  a  steady  movement  of  a  mass  of  air  eastavard  over  the  Pacific 
Ocean  to  the  Calif ornian  coast,  a  region  visited  by  the  prevailing  westerly 
winds.  The  mass  of  air  reaches  the  coast;  it  moves  on  to  the  Coast  Ranges, 
which  obstruct  the  way  to  the  east.  Air  cannot  pass  through  the  moun- 
tains; some  of  it  is  necessarily  forced  up.  The  whole  mass  of  the  atmos- 
phere does  not  move  upward,  but  the  lower  layers  are  squeezed  together 
or  compressed.  After  crossing  the  mountains,  the  air  expands  again  to 
fill  the  Great  Valley  of  California,  again  being  compressed  as  it  crosses 
the  Sierra  Nevada  Mountains.  The  compressed  air  over  the  mountain- 
tops  is  heavier  than  the  air  in  the  valleys,  and  presses  down  and  under  the 
lighter  air.  Thus,  wherever  inequalities  in  the  land  are  found,  inequalities 
in  pressure  are  established,  which  are  enough  to  start  an  upward  current 
and  a  consequent  movement  of  winds  toward  the  rising  column. 


HORSE  LATITUDE 

CALMS         /  o, 


EQUATORIAL  CALMS 


HORSE  LATITUDE 
CALMS 


PREVAILING 
WESTERLY  WINDS 


NORTH  EAST 
TRADE  WINDS 


EAST 
TRADE  WINDS 


PREVAILING 
WESTERLY  WINDS 


X 


FIG.  61 .  World  belts  of  wind  and  calm. 


An  aviator  who  flies  in  mountain  regions  becomes  very  familiar  with  the 
so-called  "holes  in  the  air"  which  are  due  to  low  pressure.  If  he  were  fly- 
ing over  California  he  would  be  borne  upward  by  the  rising  currents  on  the 
western  sides  of  the  mountains,  and  would  suddenly  drop  when  he  reached 
the  descending,  expanding  air  on  the  eastern  sides.  Clever  pilots  are  able 
so  to  circle  the  mountains  as  to  be  caught  in  the  upward  currents  and  so 
prevent  disaster. 

Winds  of  the  world.  Certain  great  wind-belts  encircle  the  globe,  mi- 
grating north  and  south  with  the  seasons.  The  part  of  the  earth  nearest 
the  equator  receives  the  greatest  amount  of  heat.  A  great  band  of  rising 
air,  known  as  the  belt  of  equatorial  calms  is  found,  therefore,  near  the  equa- 


WATER  IN  THE  AIR 


tor,  moving  northward  a  few  degrees  in  our  summer,  and  southward  in  the 
winter.  The  air  appears  calm  because  it  is  rising.  Rains  are  abundant  in 
this  belt,  because  as  the  air  rises  it  expands  and  cools,  causing  water  vapor 
to  condense  and  fall  as  rain. 

To  the  north  and  south  of  the  belt  of  equatorial  calms  are  the  trade  winds, 
steady  winds  which  blow  toward  this  belt  of  rising  air.  They  do  not  blow 
directly  north  or  south,  but  are  deflected  by  the  rotation  of  the  earth,  be- 
coming the  northeast  and  the  southeast  trade  winds.  They  are  dry  winds 
because  they  blow  constantly  toward  a  warmer  place  and  are  able,  there- 
fore, to  hold  more  moisture. 

The  horse  latitudes  are  narrow  belts  of  descending  currents  beyond  the 
trade-wind  belts.  They  are  belts  of  calms  and  drought. 

Still  farther  beyond  are  the  great  belts  of  prevailing  westerly  winds. 
These  belts  are  characterized  by  alternate  storms  and  fair  weather,  with 
the  most  frequent  winds  from  the 
west,  because  of  the  rotation  of  the 
earth.     In  these  belts  are  located 
the  most  advanced  nations. 

Foretelling  a   storm.      The 

United  States  lies  almost  en- 
tirely in  the  belt  of  the  prevail- 
ing westerly  winds.  If  you 
have  kept  a  weather  record  for 
a  few  weeks  you  have  found 
that  a  large  majority  of  the 
days  show  that  the  wind  is  from 
the  west.  These  are  usually 
the  fair  days.  Sometimes,  how- 
ever, the  wind  veers  into  the 
south  and  east.  A  storm  is 
coming,  people  say.  Sometimes 
the  storm  lasts  two  or  three 
days,  then  the  wind  changes 
into  the  west  and  the  weather 

is  fair  again.  Such  alternations  of  storms  and  fair  weather  are 
common  throughout  the  year,  but  especially  common  in  winter. 
Although  we  have  in  our  country  many  kinds  of  storms,  such  as 
thunderstorms,  windstorms,  hurricanes,  and  even  tornadoes,  by 
far  the  commonest  kind  of  storm  is  the  cyclonic  storm.  The  name 


FIG.  62.  A  storm  1200  miles  in  diameter. 
The  arrows  show  the  direction  of  the  wind. 
The  continuous  line  isobars  pass  through 
points  of  equal  pressure.  The  dotted  lines, 
isotherms,  pass  through  points  of  equal  tem- 
perature. Notice  that  winds  from  the  south 
are  warmer  than  those  from  the  north  and 
west. 


114 


WATER  AND  HOW  WE  USE  IT 


means  a  "  circle  "  or  "  whirl."  At  the  storm  center  is  a  rising 
column  of  air,  because  for  one  of  the  reasons  given  on  page  1 1 1 
an  inequality  of  pressure  has  resulted.  From  every  side  the 
heavier  air  presses  in  toward  the  storm  center.  But  instead  of 
blowing  directly  toward  the  center  the  air  is  deflected  by  the  ro- 
tation of  the  earth  toward  the  right,  forming  a  whirl  as  shown  in 
the  diagram.  The  whole  whirl,  often  covering  a  diameter  of  a 
thousand  miles,  moves  in  a  general  easterly  direction. 


FIG.  63.  Storm-tracks  across  the  United  States.     (Twenty-seven  tracks  are 
represented.)     (U.S.  Weather  Bureau.) 

Connected  with  the  passing  of  a  storm  are  other  changes  besides 
that  of  wind.  Rain  usually  falls,  because  the  rising  air  expands, 
is  cooled,  and  its  water  vapor  is  condensed.  The  temperature 
changes.  Air  from  the  south  is  warm.  Since  most  of  the  storms 
pass  to  the  north  of  the  central  and  eastern  parts  of  the  United 
States,  the  storms  in  these  sections  are  accompanied  by  south 
winds  and  rising  temperatures. 

Following  a  storm  comes  a  time  of  clear  weather,  known  as  an 
anti-cyclone.  It  is  shown  on  a  weather  map  by  an  area  of  high 
pressure.  At  the  center  air  is  settling,  bringing  to  the  earth  some 


WATER  IN  THE  AIR  115 

of  the  cool  upper  air.    In  winter  such  a  period  is  called  a  cold 
wave. 

The  path  of  storms.  For  years  the  records  of  storms  have  been 
kept.  We  can  see  from  these  records  that  certain  established 
paths  are  apt  to  be  followed.  Some  of  the  storms  reach  our 
country  from  the  Pacific.  Others  are  started  near  the  western 
mountains.  They  always  move  in  an  easterly  direction,  usually 
crossing  the  Great  Lakes,  and  following  the  St.  Lawrence  Valley 
to  the  sea.  Figure  63  shows  some  of  the  best-defined  paths. 


FIG.  64.  The  progress  of  storms  across  the  Atlantic  is  indicated  by  the  three  lines,  A,B,  and 
C,  each  of  which  marks  the  course  of  a  typical  storm  center  recorded  by  the  United  States 
Weather  Bureau.  There  are  hundreds  of  such  storms  every  year.  The  numerals  i,  2,  3,  etc., 
show  the  progress  of  the  storms  from  day  to  day.  The  rings  of  arrows  described  about  the 
storm  tracks  where  they  reach  the  European  coast  show  the  resulting  effect  upon  the  wind 
for  hundreds  of  miles  around. 

In  the  Great  War  the  direction  of  the  wind  was  of  great  importance  when  harmful  gases 
were  used.  The  arrows  show  winds  which  blew  favorably  for  the  Allies. 

(Courtesy,  Foster  Ware  and  The  Independent.) 

The  Weather  Bureau.  Upon  the  laws  which  govern  the  weather  is  based 
the  work  of  the  Weather  Bureau.  On  the  wall  in  the  forecast  room  of  the 
Weather  Bureau  at  Washington  is  an  immense  map  of  North  America  — 
twelve  feet  long  by  eight  feet  high.  The  States,  cities,  counties,  rivers, 
and  lakes  are  sketched  dimly  in  aluminum  paint.  Weather  conditions  are 
marked  on  the  map  as  they  are  received  by  telegraph.  Men  walk  up  to 
the  map  at  all  hours  of  the  day  and  mark  on  it  symbols  which  mean  rain, 
snow,  cloudiness,  heavy  winds,  fog,  hot  or  cold  waves,  or  hurricanes. 


n6  WATER  AND  HOW  WE  USE  IT 

During  the  day  every  part  of  the  map  is  reconstructed.  The  men  are  able 
to  keep  track  of  every  part  of  the  country  because  in  the  United  States 
there  are  two  hundred  branch  weather  stations;  two  hundred  and  fifty 
special  stations  which  display  danger  warnings  to  mariners;  two  hundred 
and  sixty  special  stations  for  observing  certain  conditions  of  temperature 
and  rainfall  in  the  cotton,  corn,  and  wheat  regions;  and  over  four  thousand 
stations  where  volunteer  observers  make  daily  records.  If  any  important 
change  takes  place,  the  fact  is  telegraphed  at  once  to  the  central  office,  and 
the  big  map  on  the  wall  is  altered  accordingly.  This  does  not  mean  that 
each  of  the  four  thousand  stations  is  in  individual  communication  with 
Washington.  Every  State  has  its  own  bureau,  in  which  all  messages  from 
its  own  territory  are  received,  and  at  the  discretion  of  the  State  forecaster 
are  transmitted  to  Washington.  Some  of  the  outlying  stations  are  on 
mountain-peaks,  some  are  in  the  arid  regions  of  the  Southwest,  but  all 
figuratively  are  at  the  fingers'  end  of  the  man  who  operates  the  telegraph 
sounder  in  the  corner  of  this  room  in  Washington. 

Twice  every  day,  at  8  A.M.  and  at  8  P.M.,  Washington  time,  every  tele- 
graph line  in  the  country  must  be  left  open  for  the  business  of  the  Weather 
Bureau.  At  those  hours  the  four  thousand  observers  take  an  observation 
in  their  vicinity  and  telegraph  the  result  to  their  State  centers.  Each 
State  expert  prepares  a  composite  account  of  the  State  conditions,  and 
telegraphs  them  in  code  to  Washington.  From  the  composite  accounts 
from  each  State  the  chief  forecaster  is  able  to  get  a  bird's-eye  view  of  the 
country's  weather,  and  from  his  knowledge  of  the  laws  of  weather  condi- 
tions, to  forecast  the  weather  for  several  days  in  advance. 

The  value  of  rain.  After  water  has  been  raised  above  the  sur- 
face of  the  earth  in  the  form  of  water  vapor  it  returns  to  the  earth 
again  in  the  form  of  rain.  Let  us  try  to  imagine  what  would  re- 
sult if  this  process  should  cease.  It  would  not  take  very  long 
for  the  rivers  and  streams  to  dry  up,  for  there  would  be  no  rainfall 
to  feed  them.  The  great  majority  of  places  which  are  now  fertile 
lands  would  become  barren,  for  there  would  be  no  more  water 
to  take  the  place  of  that  which  would  slowly  but  surely  disappear. 
Crops  would  not  grow,  for  the  water  in  the  soil  would  soon  all 
have  flowed  away.  The  world  would  become  almost  uninhabit- 
able except  for  a  few  living  things  that  might  continue  to  exist 
for  a  time  near  coasts  or  shores  of  lakes.  Thus  this  arrange- 
ment of  nature  by  which  water  is  evaporated  into  the  air  and 
afterwards  condensed  in  the  form  of  rain-  is  absolutely  essential 
for  the  continuation  of  life  upon  the  earth. 


WATER  IN  THE  AIR  117 

INDIVIDUAL  PROJECTS 

Working  projects: 

1.  Make  a  wind  vane. 

See  the  Book  of  Knowledge  for  directions. 

2.  Make  a  wind  wheel. 

See  Foster's  Something  to  Do,  Boys. 

3.  Several   Camp-Fire  honors   in   Campcraft   may  be  earned  by  knowing 
weather  lore,  and  keeping  scientific  records. 

4.  Make  signal  flags  and  fly  them  to  designate  the  kind  of  weather  you 
foretell. 

5.  Act  as  a  volunteer  observer  in  connection  with  the  Weather  Bureau. 

Reports: 

1.  Some  ways  of  preventing  damage  from  frost. 

Find  out  what  the  farmers,  gardeners,  and  fruit-growers  in  your  lo- 
cality do  to  protect  their  crops  from  frost.  Write  to  the  Weather  Bureau 
and  ask  for  information  about  frost-fighting.  Report  the  results  of  your 
inquiries  to  the  class. 

2.  Some  great  storms  and  the  destruction  they  have  caused. 

Find  out  from  the  local  Weather  Bureau  whether  any  great  storms  have 
wrought  destruction  in  your  locality,  and  if  they  have,  give  an  account 
of  the  damage.  Read  in  such  a  book  as  Houston's  Wonder  Book  of  the 
Atmosphere,  or  in  physical  geographies,  about  famous  storms,  and  report 
to  the  class. 

3.  How  the  weather  map  helps  a  business  man. 

An  interesting  account  of  "Doing  business  by  the  weather  map"  is 
given  in  Wonders  of  Science.  Add  to  your  report,  if  possible,  the  help  a 
business  man  in  your  town  gets  from  the  weather  map. 

4.  How  the  weather  map  helps  a  farmer. 

See  suggestions  for  3. 

5.  The  work  of  weather  experts  in  an  army. 

Go  to  the  library  to  find  magazine  articles  on  this  subject. 

6.  Man's  relation  to  climate. 

Several  pupils  may  work  on  this  project.  One  may  report  on  people 
who  live  in  cold  climates,  and  show  how  the  food,  the  homes,  and  the 
occupations  are  influenced  by  the  climate.  Other  subjects  might  be: 

The  inhabitants  of  hot  lands. 

Dwellers  in  the  desert. 

Temperate  climate  and  industry. 

BOOKS  THAT  WILL  HELP  YOU 

Africa.     F.  G.  Carpenter.     American  Book  Co. 

Contains  an  interesting  description  of  the  desert  of  Sahara. 
The  Book  of  Knowledge.     The  Grolier  Society.     New  York. 
Boy  Scouts  of  America.     Official  Handbook.     Doubleday,  Page  &  Co. 
"  Reading  the  Weather."     T.  H.  Longstreth.     Outing.     1915. 

A  lively  account  of  how  weather  is  made  and  foretold. 
Something  to  Do,  Boys.     E.  A.  Foster.     W.  A.  Wilde  Co. 

Directions  for  making  a  wind  wheel  are  included. 
South  America.     N.  B.  Allen.     Ginn  &  Co. 

An  account  of  modern  conditions  in  South  America. 


ii8  WATER  AND  HOW  WE  USE  IT 

The  Wonder  Book  of  the  Atmosphere.     E.  J.  Houston.     Fred.  A.  Stokes  Co. 
Wonders  of  Science.     E.  M.  Tappan,  Editor.     Houghton  Mifflin  Co. 
Weather  Series  for  the  Amateur.     P.  R.  Jameson.     Taylor  Instrument  Com- 
panies.    Rochester,  New  York. 

Practical  Hints  for  Amateur  Weather  Forecasters. 

Humidity,  its  Effect  on  our  Health  and  Comfort. 

The  Mountains  of  Cloudland  and  Rainfall.    " 

The  Barometer  as  the  Footrule  of  the  Air. 

Weather  and  Weather  Instruments. 
General  Science  Quarterly.     W.  G.  Whitman,  Editor.     Salem,  Massachusetts. 

The  January,  1918,  number  contains  a  good  article  on  "Science  in  the 
War." 


PROJECT  VII  . 
WATER  AND  THE  SOIL 

How  soil  is  made.  The  story  of  how  soil  is  made  is  one  of 
the  wonder-tales  of  nature.  Perhaps  you  may  think  of  soil  as 
"  nothing  but  dirt,"  and  brush  it  from  your  hands  with  disgust 
when  you  handle  it.  When  you  realize  the  mighty  forces  that 
have  entered  into  its  making,  and  the  mighty  work  that  it  does 
for  the  living  world,  you  will  look  upon  it  with  respect. 


FIG.  65,  From  mountain-top  to  soil.  The  action  of  weather  and  of  running  water 
have  brought  down  much  material  from  the  bare  mountain  sides  to  form  soil  in  the 
fertile  valley. 

The  value  of  water  in  the  soil.  We  shall  learn  as  we  undertake 
this  project  something  of  the  valuable  rocks  that  crumble  to  soil. 
We  shall  find  out  how  the  forces  of  nature  bring  about  a  trans- 
formation of  a  barren  mountain-top  into  the  soil  of  a  fertile  valley. 
Yet  no  matter  how  valuable  the  mineral  matter  of  the  soil  is,  it  is 


I2O 


WATER  AND  HOW  WE  USE  IT 


of  no  value  to  man  until  its  wealth  is  unlocked  by  the  power  of 
water.  Only  mineral  matter  in  solution  can  enter  into  the  roots 
of  plants  and  cause  them  to  grow.  The  Sahara  Desert  can  pre- 
sent all  the  contrast  of  a  barren,  sand-swept  waste  and  a  blossom- 
ing oasis ;  the  only  difference  is  the  absence  or  the  presence  of 
water. 


FIG.  66.  A  desert  spring. 
(Courtesy,  Burton  Holmes.) 

The  problems  which  follow  will  give  you  an  opportunity  to  ob- 
tain first-hand  knowledge  as  to  the  soil.  Go  out  and  see  how  the 
forces  of  nature  are  working  every  day  to  transform  the  rocks  in 
your  neighborhood  into  soil  (problem  i).  If  you  have  a  garden, 
even  if  it  is  no  larger  than  a  window  box,  problems  2—9  will  give 
you  many  suggestions  for  improving  your  treatment  of  the  soil. 
The  same  problems  will  show  you  some  of  the  reasons  why  plants 
can  be  transformed  in  a  few  weeks  from  dry  seeds  into  juicy  stalks 
with  leaves  and  fruits. 


WATER  AND  THE  SOIL  121 

PROBLEMS 

PROBLEM  i :  A  FIELD  TRIP  TO  STUDY  THE  FORMATION  OF  SOIL. 

Directions: 

If  possible,  go  to  the  open  country,  where  you  can  find  a  stream.  If  you 
cannot  go  to  the  country,  however,  you  can  find  the  answers  to  most  of  the 
questions  in  your  own  back  yard  and  along  the  streets. 

Find  a  place  where  the  land  has  been  cut  away,  as  in  a  railroad  cut,  or  a 
sandbank.  How  deep  is  the  soil?  What  are  the  colors  of  the  soil  and  of 
the  subsoil? 

Look  for  the  action  of  water.  What  happens  along  the  banks  of  streams  ? 
Find  a  place  where  the  stream  bends.  What  is  the  action  of  the  water  on 
the  earth  at  the  outer  side  of  the  bend?  at  the  inner  side?  Examine  the 
pebbles  in  the  stream-bed.  Account  for  their  shape.  What  becomes  of 
the  material  worn  off  from  the  pebbles? 

If  there  are  hills  in  the  region,  look  for  the  action  of  water  in  wearing 
away  the  soil.  Is  the  soil  washed  away  more  on  a  grassy  hill,  a  road, 
ploughed  ground,  or  a  wooded  hillside?  How  do  you  account  for  the 
differences? 

Look  for  the  action  of  the  wind.  Is  the  dust  blowing?  Where  does  it 
come  from?  Where  does  it  go? 

Look  for  the  action  of  plants.  Examine  some  soil  to  see  if  it  contains 
any  parts  of  plants.  Can  you  find  any  places  covered  by  weeds?  What 
becomes  of  the  weeds?  What  becomes  of  the  leaves  that  fall  from  the 
trees? 

Look  for  the  action  of  animals.  Can  you  find  earthworm  burrows  or 
the  earthworms  themselves?  Are  earthworms  of  any  use  in  the  soil?  Can 
you  find  any  insects?  What  becomes  of  their  dead  bodies?  If  the  land 
is  used  for  a  pasture,  look  for  manure  left  by  horses,  cows,  or  sheep.  Is 
it  of  value  to  the  soil? 

Look  for  the  action  of  the  air.  Can  you  find  rocks  which  appear  rusty? 
What  gas  in  the  air  causes  iron  to  rust?  Iron  is  abundant  in  rocks.  Can 
you  find  places  where  the  rocks  are  crumbling  on  the  outside,  because  of 
the  action  of  the  weather? 

Summary: 

Write 'a  composition  about  your  trip,  including  all  you  have  learned 
about  soil  formation.  Make  diagrams  to  illustrate. 

PROBLEM  2:  WHAT  DOES  SOIL  CONTAIN? 

Directions: 

Find  some  soil  which  seems  perfectly  dry.  Heat  a  little  in  a  test-tube. 
What  comes  from  it? 

Fill  a  glass  about  half  full  of  soil.     Add  water  to  within  an  inch  of  the 


122  WATER  AND  HOW  WE  U§E  IT 

top.     Watch  the  glass  for  several  minutes,  while  it  stands  quietly  on  the 
table.     What  comes  from  the  soil? 

Stir  the  soil  and  the  water  thoroughly,  and  let  it  settle.  After  it  has 
settled  so  that  the  water  above  it  is  practically  clear,  describe  the  appear- 
ance. Can  you  distinguish  between  the  sand,  the  clay,  and  the  humus  ? 

Summary: 

Name  five  materials  found  in  soil. 

PROBLEM  3:  How  DO  SOILS  DIFFER  IN  THEIR  ABILITY  TO  HOLD  WATER? 

Directions: 

Use  flower  pots  of  the  right  size  to  fit  into  the  tops  of  tumblers.  Fill  the 
pots  with  different  kinds  of  soil  which  must  be  dry:  —  pure  sand,  sandy 
loam,  clayey  loam,  rich  garden  soil,  manure,  leaf  mold,  etc. 

Stand  each  pot  in  a  tumbler.  Fill  a  graduate  with  water,  taking  care 
that  the  water  just  reaches  the  top  mark.  From  the  graduate  pour  some 
of  the  water  into  a  large  salt  shaker,  and  from  it  sprinkle  water  slowly  on 
the  surface  of  the  soil  in  the  first  pot.  As  soon  as  the  water  begins  to  drip 
into  the  glass,  stop  sprinkling,  and  pour  back  into  the  graduate  any  unused 
water. 

How  much  water  did  the  soil  absorb  before  allowing  any  to  pass  through? 

In  the  same  way  sprinkle  water  into  each  pot,  and  keep  a  tabular  record 
of  the  amount  of  water  absorbed  by  each  kind  of  soil. 

Summary  : 

Name  the  kinds  of  soil  tested  in  the  order  of  their  water-holding  capacity. 

PROBLEM  4:  CAN  FINE  OR  COARSE  SOIL  HOLD  MORE  WATER? 

Directions: 

Dip  a  pebble  in  water.  Shake  off  the  water.  What  clings  to  the  sur- 
face? Watch  and  explain  its  final  disappearance. 

In  one  scale  pan  of  a  delicate  balance  place  a  large  stone.  Balance  with 
small  pebbles  on  another  scale  pan. 

Compare  the  surface  exposure  of  the  large  stone  with  the  surface  ex- 
posure of  the  small  pebbles. 

Wet  the  stones  and  replace  in  the  balance.  Compare  the  weight  of 
water  held  as  a  surface  film  by  the  large  stone  with  the  weight  of  water 
held  by  the  many  small  pebbles. 

Conclusions: 

1.  What  clings  to  the  surface  of  each  soil  particle? 

2.  Can  fine  or  coarse  soil  hold  more  water? 

PROBLEM  5 :  How  DOES  WATER  RISE  IN  THE  SOIL? 

Directions: 

Put  a  small  glass  tube  in  a  glass  of  water  colored  with  red  ink.  Is  the 
level  of  the  water  the  same  in  the  glass  and  in  the  tube? 


WATER  AND  THE  SOIL  123 

Make  tubes  of  different  sizes.  To  do  this,  heat  the  glass  tubing  slowly 
in  a  flame,  constantly  rotating  it  until  the  glass  is  soft  enough  to  pull. 
Then  remove  the  tube  from  the  flame  and  carefully  pull  the  two  ends  apart. 
When  cool,  cut  by  marking  with 
a  triangular  file  and  snapping  the 
glass  at  that  point. 

Try  tubes  of  different  sizes  to 
find  out  if  water  rises  higher  in 
a  wide  or  narrow  tube. 

(Note  — •  Narrow   tubes  are 

called  capillary  tubes,  from  the 

Latin  word  "capilla,"  a  hair.) 

Put  a  lamp  wick  into  a  glass  FIG.  67.  Making  capillary  tubes, 

of  water  colored  with  red  ink, 

allowing  the  end  to  hang  over  into  another  glass.  What  happens?  Try 
the  same  experiment  with  a  narrow  strip  of  blotting-paper.  Explain  the 
reason  for  the  results. 

Make  a  lamp  as  follows:  Fill  a  small  bottle  about  one  third  full  of  kero- 
sene oil.  Fill  the  bottle  to  the  top  with  small  fragments  of  dry  earth. 
What  happens  to  the  oil?  After  a  few  minutes  (Caution  /)  touch  a  lighted 
match  to  the  surface  of  the  earth.  Explain  what  happens. 

Question: 

In  what  respects  are  these  experiments  alike? 

Conclusion: 
How  can  underground  water  reach  the  surface  of  the  soil? 

PROBLEM  6:  WHAT  is  THE  VALUE  OF  A  FINE  SURFACE  LAYER  OF  SOIL? 

Directions: 

On  top  of  a  cube  of  ordinary  loaf  sugar  heap  powdered  sugar  about  a 
quarter  of  an  inch  deep?  Which  represents  the  "dust  mulch"  on  the 
surface?  Which  represents  the  soil? 

Into  a  small  dish,  such  as  a  butter  plate,  pour  a  little  water  colored  with 
red  ink.  Place  the  cube  of  sugar  in  this  liquid. 

How  long  does  it  take  the  liquid  to  reach  the  top  of  the  loaf  sugar? 
Explain  why  it  climbs  up. 

How  long  does  it  take  the  liquid  to  reach  the  top  of  the  powdered  sugar? 
Why? 

Conclusion: 
What  is  the  value  of  a  fine  surface  layer? 

Questions: 

1.  How  would  you  make  a  dust  mulch? 

2.  In  a  seed-bed  where  should  the  soil  be  packed  firmly  and  where  left 
loose? 


124  WATER  AND  HOW  WE  USE  IT 

PROBLEM  7:  How  MAY  THE  MOISTURE  IN  THE  SOIL  BE  KEPT  FROM 
ESCAPING? 

Directions: 

Have  ready  some  fine  dry  soil  which  has  been  sifted  through  a  flour 
sieve. 

Set  two  lamp  chimneys  in  a  pan  or  dish. 

By  means  of  a  creased  paper  pour  the  fine  soil  into  one  lamp  chimney 
halfway  to  the  top  and  pack  it  firmly. 

Fill  the  other  chimney  one  third  full  with  the  fine  soil;  pack;  then  add 
enough  loose  soil  to  bring  the  level  to  that  of  the  first  chimney. 

Pour  water  into  the  pan,  and  watch  results. 

In  which  chimney  does  the  water  reach  the  top  first? 

Conclusion: 

Does  water  rise  more  rapidly  in  packed  or  loose  soil? 

Questions: 

1.  How  can  moisture  in  the  soil  be  kept  from  evaporating? 

2.  Is  it  better  to  water  your  garden  every  day  or  to  stir  the  surface  of 
the  soil  often?     Why? 

PROBLEM  8:  Is  THE  SOIL  IN  MY  GARDEN  ACID? 

Directions: 

Put  a  little  soil  in  a  glass.  Add  enough  water  to  make  a  thin  mud. 
Dip  a  piece  of  blue  litmus  paper  into  the  mud. 

Remove  the  paper  and  wash  off  the  mud.     Has  it  changed  color? 

Test  to  find  whether  water  alone  causes  the  same  appearance. 

Where  was  the  substance  which  caused  the  change,  if  any  appeared? 

(Litmus  paper  is  colored  with  a  dye  which  is  sensitive  to  acid.  Acid 
turns  blue  litmus  paper  red.) 

Conclusion: 

Is  the  soil  which  you  tested  acid  or  not? 

PROBLEM  9:  How  MAY  ACIDITY  IN  SOIL  BE  CORRECTED? 

Directions: 

Put  a  little  dilute  acid  in  a  test-tube.  Test  it  with  litmus  paper.  Add 
a  little  powdered  lime.  What  happens? 

Add  more  lime  until  all  action  stops.  Test  again  with  litmus  paper. 
Account  for  the  results. 

Conclusion: 
What  substance  neutralizes  acid;  i.e.,  causes  it  to  lose  its  acidity? 

Question: 

How  may  the  acidity  in  soil  be  corrected? 


WATER  AND  THE  SOIL 


125 


FIG.  68.  The  most  important 
elements  in  the  soil:  Al,  aluminum; 
Ca,  calcium;  Mg,  magnesium;  Na, 
sodium;  K,  potassium. 


What  soil  contains.  When  we  separate  soil  into  its  parts  we 
find  that  it  consists  of  small  rock  particles  of  various  sizes.     The 
smallest  particles  are  called  clay;  they  are  so  small  that  four 
hundred  thousand  of  them,  set  in  a 
line,  measure   only  one   inch.    They 
are  the  particles  that  are  rubbed  from 
the  surfaces  of  rocks  as   they  grind 
against  each  other. 

Larger  particles  can  easily  be  seen ; 
they  vary  in  size  from  the  fine  clay  to 
coarse  gravel ;  they  are  called  sand. 

In  addition  to  the  rock  particles, 
soil  usually  contains  humus,  which 
consists  of  decaying  vegetable  or  ani- 
mal matter. 

Even  dry  soil  contains  some  water, 
which  clings  as  a  film  to  each  little 
particle  of  clay  and  sand. 

Between  all  the  particles,  no  matter  how  closely  packed,  are 
spaces  which  contain  air. 

Rocks.  All  the  rock  particles  in  the  soil  have  been  formed  from 
solid  rock.  Some  day  you  may  study  the  science  of  geology,  which 
treats  of  the  formation  of  our  earth,  and  the  rocks  which  compose 
it.  Even  now  you  can  learn  something  of  the  kinds  and  charac- 
teristics of  rocks. 

Geologists  divide  all  the  rocks  of  the  world  into  three  great 
classes,  igneous,  sedimentary,  and  metamorphic.  Those  names 
look  very  long  and  hard  to  remember,  but  when  you  know  what 
the  names  mean,  you  will  remember  them  easily. 

Igneous  rocks.  Igneous  rocks  are  fire-formed  rocks.  "  Ignis  " 
is  the  Latin  word  for  fire.  As  in  so  many  other  cases,  English- 
speaking  people  have  used  a  Latin  word  to  make  an  English  word. 
All  rock  which  has  hardened  from  hot  molten  matter  is  called 
igneous  rock. 

One  common  kind  of  igneous  rock  is  granite.  It  is  composed 
of  crystals  of  three  or  four  different  minerals,  which  can  plainly 
be  seen.  Granite  is  a  very  hard  rock,  and  is  often  left  standing 


126 


WATER  AND  HOW  WE  USE  IT 


as  a  mountain-peak,  from  which  the  softer  rocks  have  been  worn 
away.     It  is  very  common  in  New  England. 

Another  class  of  igneous  rock  has  been  formed  by  volcanic 
action.  Even  now  some  volcanoes  occasionally  send  out  great 
rivers  of  molten  lava  which  hardens  into  rock.  In  ages  past  vol- 
canoes have  been  much  more  active  than  they  are  now.  In  some 
parts  of  the  world  great  lava  floods  have  flowed  out  from  cracks 
in  the  earth's  surface.  The  Palisades  of  the  Hudson,  the  hills 
of  New  Jersey  and  of  the  Connecticut  Valley,  parts  of  Yellow- 
stone Park,  and  the  Snake  River 
and  Columbia  River  Valleys,  in 
Washington,  Oregon,  and  Idaho, 
are  a  few  of  the  places  in  our 
own  country  composed  of  hard- 
ened lava. 

About  one  tenth  of  the  surface 
of  the  earth  is  igneous  rock,  and 
where  other  rocks  are  on  the 
surface,  igneous  rocks  are  under- 
neath. 

Sedimentary  rocks.  If  you 
have  visited  the  beach,  you  have 
noticed  that  it  is  composed  of 
layers  of  coarse  rocks,  of  gravel, 
of  sand,  and,  on  the  "  flats  "  at 
low  tide,  of  mud.  Perhaps  you 
have  dug  down  through  the 
sand  and  found  layers  of  other 
material  below.  All  these  ma- 
terials have  been  deposited  by 
the  water.  The  material  carried 
by  water  is  called  sediment. 

Again,  you  may  have  seen  places  where  rivers  have  overflowed 
their  banks  and  left  layers  of  muddy  slime  on  the  surface  of  the 
ground.  You  have  heard  of  how  the  Nile  River  has  overflowed 
its  banks  every  year  for  thousands  of  years,  and  of  how  the 
farmers  depend  upon  the  mud  left  behind  to  fertilize  their  fields. 
The  mud  is  the  sediment  carried  by  the  river. 


FIG.  69.  A  gorge  cut  in  shale.  The  small 
stream  has  cut  a  deep  gorge  through  the 
horizontal  layers  of  soft  shale.  The  val- 
ley is  being  widened  by  the  action  of 
plants  and  of  ground  water  which  seeps 
through  the  rocks  at  the  side. 


WATER  AND  THE  SOIL 


127 


How  do  the  layers  of  mud,  sand,  gravel,  and  rock  deposited 
by  streams  and  the  ocean  become  hardened  into  solid  rock?  We 
must  realize  that  this  action  has  been  g<9ing  on  for  thousands  and 
thousands  of  years.  One  layer  of  sediment  is  laid  on  another. 
The  pressure,  with  the  cementing  action  of  certain  minerals  in  the 
water,  gradually  hardens  the  layers  to  form  sedimentary  rock. 

Four  common  kinds  of  sedimentary  rock  are  easy  to  recognize. 

Shale  is  a  fine-grained  rock  made  of  hardened  clay. 

Sandstone  is  a  coarser-grained  rock  made  of  grains  of  sand  ce- 
mented together. 

Puddingstone  is  made  of  a  mixture  of  fine  mud  and  large  pebbles 
scattered,  like  plums  in 
a  pudding,  throughout 
the  mass. 

Limestone  is  made  of 
the  limy  Skeletons  of 
tiny  animals  who  lived 
in  the  sea,  and  whose 
shells  dropped  to  the 
bottom  when  they  died. 

Metamorphic  rocks. 
Metamorphic  rocks  are 
those  which  have  been 
changed  from  one  kind 
to  another.  The  agents 
which  have  produced 
the  changes  are  (i)  great  pressure,  and  (2)  the  action  of  heated 
water. 

Soft  shale  may  be  changed  to  slate,  a  much  harder  rock  which 
splits  into  smooth  slabs. 

Sandstone  may  be  changed  to  quartzite,  a  rock  in  which  every 
grain  of  sand  is  surrounded  with  the  mineral  quartz. 

Limestone  may  be  changed  to  marble,  composed  of  beautiful 
crystals. 

Soft  coal,  a  rock  containing  a  great  deal  of  carbon,  may  be 
changed  to  hard  or  anthracite  coal. 

The  action  of  water  in  making  soil.    Some  of  the  forces  which 


FIG.  70.  Layers  of  metamorphic  rock  pressed  out  of 
shape  by  great  changes  in  the  earth's  crust.  The  black 
layers  are  hard  coal.  (From  Greene's  Coal  and  Coal 
Mines.} 


128 


WATER  AND  HOW  WE  USE  IT 


FIG.  71.  A  diagram  of  an  anthracite  coal  mine.    Coal  occurs  in  layers  between  other 
metamorphic  rocks,  such  as  slate. 

* 

make  soil  can  be  seen  at  work  every  day.  The  first  is  water.  After 
a  rain  you  can  see  the  little  streams  of  water  making  their  way 
down  the  slopes,  tearing  away  small  rocks  and  pebbles,  rolling 


FIG.  72.  Action  of  running  water.  The  erosion  of  the  running  water  can  be  seen  along  the 
banks.  The  rock  is  smoothed  and  holes  are  worn  at  flood  time  by  the  grinding  action  pf 
smajl  stones. 


WATER  AND  THE  SOIL 


129 


them  down  the  gullies,  rubbing  and  scraping  them  against  each 
other.  You  cannot  see  that  the  rocks  thus  torn  away  and  carried 
by  the  water  are  any  smaller  than  they  were  before ;  but  imagine 
such  action  going  on  month  after  month,  year  after  year,  century 
after  century.  Can  you 
understand  how  in  time 
many  rocks  are  rubbed 
to  powder,  which  becomes 
a  part  of  the  soil? 

What  can  be  seen  on 
a  small  scale  after  any 
rain  is  constantly  going 
on  as  a  result  of  river  ac- 
tion. Even  a  small  brook 
will  wear  away  the  bank 
on  one  side,  and  build  up 
the  other  side  by  deposit- 
ing there  sand  and  clay 
which  has  been  torn  away 
somewhere  up  the  stream. 
Such  great  rivers  as  the 
Yellowstone  have  cutdeep 
canyons  by  wearing  away 
the  solid  rock,  bit  by  bit. 
Much  of  the  material 

which  once  filled  those  canyons  has  gone  into  the  making  of  soil 
somewhere,  or  has  been  carried  out  to  sea. 

Different  kinds  of  rock  show  a  difference  in  the  resistance  which 
they  offer  to  the  wearing  away  by  water,  or  erosion,  as  the  process 
is  called.  Soft  rocks,  like  shale,  sandstone,  and  limestone,  are 
quite  easily  worn  away,  while  hard,  crystalline  rocks,  like  granite, 
resist  the  action  of  the  water  much  longer.  Sometimes  an  unusu- 
ally hard  place  in  a  rock  may  cause  such  peculiar  effects  as  the 
pinnacles  shown  in  figure  73- 

Soil  built  up  by  the  action  of  rivers  is  called  alluvium.  It  is 
usually  fertile  because  the  sediment  deposited  by  the  water  con- 
sists of  fine  particles  of  various  kinds  of  rocks.  New  deposits 


FIG.  73.  The  result  of  weathering  and  water  erosion. 


130 


WATER  AND  HOW  WE  USE  IT 


enrich  the  soil  constantly.  So  rich  is  alluvial  soil  in  the  minerals 
necessary  for  plant  growth  that  the  application  of  fertilizers  is 
usually  unnecessary.  Some  of  the  earliest  civilizations  of  the 
globe  grew  up  along  the  flood-plains  of  rivers,  and  on  the  deltas 

deposited  at  their  mouths. 
In  Egypt  the  people  who 
lived  on  the  fertile  delta 
and  in  the  flood-plain  of 
the  Nile  had  attained  a 
high  degree  of  civilization 
long  before  the  Christian 
era.  China  was  able  to 
support  herself  for  centu- 
ries, a  nation  apart  from 
the  world,  largely  because 
of  the  intensive  farming 
which  her  people  practiced 
on  the  fertile  plains  of  the 
Yellow  and  the  Yangtse 
Rivers. 

The  action  of  ice.  All 
over  New  England  and 
over  much  of  the  rest  of 

FIG.  74.  Ancient  ice  sheets  in  North  America,  the  northern  part  of  the 
The  ice  advanced  from  several  centers.  Notice  the  United  States  the  soil 
limit  reached  by  the  great  glacier.  .  . 

shows  the  action  of  ice. 

Scattered  through  the  soil  are  rocks  and  boulders  of  various 
sizes,  often  composed  of  kinds  of  rock  very  different  from  the 
bed-rock  of  the  vicinity.  These  rocks  have  evidently  been 
brought  by  some  great  agent  strong  enough  to  move  huge  loads. 
We  know  that  that  agent  was  ice.  Many  thousands  of  years  ago 
extensive  ice-sheets  or  glaciers  covered  much  of  the  northerly  por- 
tions of  the  earth.  They  flowed  out  from  certain  centers,  shearing 
off  rocks  and  loose  soil  as  they  came,  grinding  pebbles  to  fine 
clay  by  their  great  weight,  leveling  off  some  of  the  heights  and 
filling  in  the  hollows.  Finally  the  ice  melted,  and  the  load  of 
boulders,  rocks,  pebbles,  sand,  and  clay  was  left  scattered  over  the 


WATER  AND  THE  SOIL  131 

surface.  As  vegetation  grew  up,  the  top  layers  became  darker 
because  of  the  parts  of  plants  left  in  the  earth,  and  a  true  glacial 
soil  was  formed. 

Another  kind  of  ice  action  goes  on  every  winter.  Water  collects 
in  little  cracks  and  holes  in  rocks,  and  then  freezes.  The  expan- 
sion of  the  water  into  ice  cracks  the  rock,  so  that  it  breaks.  Such 
ice  action  can  be  seen  very  plainly  on  mountain-tops  above  the 
timber-line.  Clay  soil  which  has  caked  is  often  crumbled  thus  by 
the  frost. 

The  action  of  wind.  Another  force  constantly  at  work  in  mak- 
ing soil  is  the  wind.  Fine  particles  are  caught  up  by  the  wind  and 
are  often  carried  long  distances  before  being  dropped  again.  Where 
have  you  seen  soil  built  up  by  the  wind?  It  is  said  that  about 
half  of  the  State  of  Nebraska  is  covered  with  soil  made  by  the 
wind's  removal  of  particles  from  the  other  half.  The  fertile  "  loess  " 
of  China,  thousands  of  feet  in  thickness  in  places,  has  been  made 
by  the  westerly  winds  blowing  fine  dust  into  that  country  from 
the  dry  parts  of  Siberia  and  neighboring  regions.  Can  you  ex- 
plain why  grass  is  sometimes  planted  on  sand  dunes? 

The  action  of  air.  One  of  the  common  elements  in  rocks  is  iron. 
You  know  how  an  iron  nail,  if  exposed  to  the  air,  soon  rusts.  In 
much  the  same  way  the  iron  in  rocks  is  oxidized  and  changed  to  a 
reddish  powder,  which  is  easily  washed  away  by  the  rain  and 
by  running  water.  The  remaining  particles  of  rock  therefore 
crumble  to  soil. 

The  temperature  of  the  air  also  helps  to  form  soil.  Warming 
causes  rocks  to  expand,  and  cooling  causes  them  to  contract,  es- 
pecially near  the  surface.  Such  changes  cause  the  surface  to 
scale  off  in  time,  and  crumble  to  soil. 

The  warm,  dry  air  of  desert  countries  produces  changes  much 
more  slowly  than  the  moist  air  of  more  temperate  countries.  A 
famous  example  showing  the  difference  is  the  change  in  an  obelisk 
which  had  stood  for  over  three  thousand  years  in  Egypt  without 
crumbling.  It  was  brought  to  New  York,  where  the  damp  cli- 
mate, with  cold  winters  and  hot  summers,  caused  it  to  decay  so 
quickly  that  it  had  to  be  protected  with  a  surface  layer  of  a 
glassy  substance. 


132  WATER  AND  HOW  WE  USE  IT 

The  action  of  plants.  Soil  which  consists  of  pure  rock  mate- 
rial like  sand  and  clay  is  not  "  rich."  It  is  humus  that  makes  the 
soil  rich.  Much  of  the  humus  comes  from  plants  which  have 
grown  previously  in  the  soil.  Notice  the  soil  in  a  pine  woods 
which  has  not  been  cultivated  for  years;  is" it  dark  or  light?  Soil 
which  contains  humus  is  usually  dark ;  we  can  often  tell  its  richness 
by  its  color.  Even  weeds,  usually  considered  only  as  the  farm- 
ers' enemies,  may  be  slightly  helpful  by  adding  their  decaying 
bodies  to  the  soil. 

"  Green  manuring  "  is  the  process  of  adding  humus  to  the  soil 
by  letting  such  plants  as  clover  or  winter  rye  grow  for  a  while 
and  then  ploughing  them  in.  Why  is  it  better  to  put  dead  leaves 
on  a  compost  pile  than  to  burn  them? 

The  most  valuable  plants  in  the  soil  are  invisible.  They  are 
the  bacteria  which  produce  decay  and  which  so  change  the  humus 
that  it  loses  its  form  and  is  made  into  a  part  of  the  soil  itself. 
Only  recently  have  people  come  to  understand  the  great  good  done 
by  the  bacteria  in  the  soil. 

The  action  of  animals.  Whenever  we  dig  in  the  garden  we  are 
aware  that  the  soil  is  the  home  of  many  animals.  Rich  soil  is 
the  home  of  earthworms.  Do  not  kill  earthworms  as  you  kill 
other  "  worms."  They  are  our  friends.  An  earthworm  acts  like 
a  tiny  plough,  eating  its  way  through  the  soil.  Much  of  the  loam 
in  the  garden  has  been  prepared  by  being  passed  through  the 
bodies  of  earthworms.  One  of  the  greatest  scientists  of  the  nine- 
teenth century,  Charles  Darwin,  made  a  very  careful  study  of  their 
habits  and  the  good  they  do,  the  results  of  which  he  published  in 
a  book,  Vegetable  Mold  and  Earthworms. 

Even  injurious  insects  like  cutworms,  wireworms,  and  maggots, 
which  live  in  the  ground,  may  do  a  little  good  to  the  soil  by  fur- 
nishing their  dead  bodies  to  add  to  the  humus.  Indeed,  the  only 
good  they  do  is  after  their  death,  so  kill  them  whenever  you  have 
an  opportunity. 

Another  way  in  which  animals  help  the  soil  is  in  furnishing  ma- 
nure. In  the  Government  experiment  stations  it  has  been  found 
that  some  of  the  most  profitable  farms  are  those  on  which  live- 
stock are  raised,  since  they  not  only  bring  a  good  price,  but  en- 
rich the  soil  for  the  growing  of  plants. 


WATER  AND  THE  SOIL 


133 


Plants  need  water.  We  know  that  water  is  used  by  the  human 
body  to  help  to  take  in  foods  and  give  off  wastes.  The  same  thing 
is  true  of  plants.  Water  dissolves  some  of  the  mineral  matter 
so  that  it  can  be  taken  up  by  the  roots.  Water  helps  seeds  to 
sprout  and  plants  to  grow.  It  is  true  that  some  living  things 


BU. 
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1892  TO  1907 
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can  continue  to  exist  for  rather  long  periods  of  time  without  water. 
Under  these  conditions,  however,  they  usually  go  into  a  resting 
state  in  which  they  are  in  a  certain  sense  dead,  since  they  carry 
on  life-activities  in  a  very  slow  sort  of  fashion,  if  at  all.  Thus 
bacteria  of  some  kinds  may  remain  alive  in  the  dust  for  many 
months.  Some  kinds  of  seeds  may  remain  alive  for  several  years 
without  any  water.  This  is  shown  by  the  fact  that  they  retain 
their  power  to  sprout.  These  seeds  are  not,  however,  abso- 
lutely dry,  for  their  tough  coats  retain  some  moisture  inside.  It 
has  been  found  that  if  they  are  completely  dried  by  artificial  means 
they  will  be  killed,  and  will  not  sprout  when  planted. 
Water  in  the  soil.  Soils  differ  in  their  ability  to  retain  water. 


134  WATER  AND  HOW  WE  USE  IT 

Some  kinds  permit  the  water  to  soak  slowly  through  them,  while 
others  dry  out  soon.  All  kinds  of  soils  are  more  or  less  porous; 
that  is,  air  is  present  between  the  soil  particles.  Around  each 
soil  particle,  even  in  apparently  dry  soil,  is  a  film  of  water. 
When  anything  is  divided  into  smaller  parts  the  surface  is  in- 
creased. Since  every  soil  particle  is  covered  with  a  film  of  water, 
the  smaller  the  particles  are,  the  greater  the  amount  of  water 
which  can  be  held  in  readiness  for  the  little  roots  to  absorb. 

Soil  is  named  from  the  kind  of  material  most  prominent  in  it; 
as  sandy  loam,  medium  loam,  clay  loam,  etc.  It  is  plain  that  the 
sandy  loam,  being  the  coarsest,  has  the  fewest  soil  particles,  and 
that  the  clay  loam  has  the  most.  Clay  loam  can,  therefore,  hold 
more  water  than  sandy  loam;  it  is  slower  in  drying,  and  cannot 
be  worked  so  early  in  the  spring. 

Manure  and  leaf  mold  can  hold  more  water  than  any  of  the 
rock  soils.  This  is  because  they  not  only  hold  water  on  their  sur- 
faces, but  also  absorb  it  like  a  sponge.  One  reason  why  manure  is 
beneficial  to  the  soil  is  that  it  makes  the  soil  hold  more  water. 
The  variety  of  soil  that  is  favorable  for  most  plants  upon  which 
man  depends  for  his  foods  is  a  soil  in  which  the  pores  are  neither 
too  large  nor  too  small;  which  is  neither  too  sandy  nor  too  clayey. 

How  water  rises  in  the  soil.  Not  only  does  water  drain  away 
through  the  soil  after  a  rain;  it  also  rises  through  the  soil.  If  you 
dig  down  far  enough,  you  will  find  a  place  where  water  stands  all 
the  time.  This  is  called  the  water  table.  Sometimes  it  is  near 
the  surface  or  even  above  the  surface,  as  in  swampy  land.  Some- 
times it  is  far  below  the  surface.  The  height  of  the  water  table 
may  be  seen  wherever  there  is  a  well,  by  seeing  how  near  the  sur- 
face the  water  stands.  The  height  varies  according  to  the  season. 
Why  do  some  wells  dry  up  in  the  summer? 

After  a  rain  most  of  the  water  soon  drains  away  to  the  water 
table,  leaving  only  the  little  films  of  water  on  the  soil  particles. 
This  water  can  creep  through  the  soil  in  the  little  spaces,  just  as 
oil  can  creep  up  a  lamp  wick,  or  ink  can  soak  into  a  blotter. 
The  creeping-up  is  called  capillary  action. 

The  smaller  the  space,  the  higher  the  water  can  creep.  It  rises, 
therefore,  more  easily  in  clayey  loam  than  in  sandy  loam.  When 


WATER  AND  THE  SOIL  135 

the  water  reaches  the  surface,  some  of  it  evaporates  into  the 


air. 


How  to  save  the  moisture  in  the  soil.  One  of  the  problems  of 
every  farmer  and  gardener  is  to  prevent  too  much  evaporation 
from  his  land,  with  a  consequent  loss  of  valuable  water.  When 
water  evaporates  from  the  surface,  more  water  creeps  up  to  take 
its  place,  causing  the  soil  finally  to  dry  out  unless  Waporation  is 
checked. 

One  of  the  best  ways  of  preventing  too  much  evaporation  is  to 
provide  a  surface  mulch.  The  mulch  is  light  covering  of  some 


FIG.  76.  A  rainfall  map.  The  greatest  rainfall  in  the  world  is  near  the  equator. 
In  the  belts  of  prevailing  westerly  winds  the  greatest  precipitation  is  on  the 
western  side  of  continents.  Compare  this  map  with  figure  60. 

kind.  Sometimes  old,  dry  manure  is  put  around  plants.  Sometimes 
straw  is  laid  on  the  bare  ground  of  a  potato  patch  or  a  strawberry 
bed.  The  cheapest  and  simplest  way  is  merely  to  stir  the  soil 
after  a  rain  to  a  depth  of  about  two  inches.  The  loose  soil  soon 
dries  and  crumbles  to  dust,  which  prevents  the  water  below  from 
evaporating.  We  cultivate  the  soil  after  a  rain  to  form  this 
dust  mulch.  A  dust  mulch  prevents  evaporation  because  the 
spaces  between  the  particles  of  soil  are  made  larger,  and  capillary 
action  is  hindered. 


136 


WATER  AND  HOW  WE  USE  IT 


FIG.  77.  United  States  Government  Reclamation 
Projects.  Each  project  requires  great  expenditure  of 
labor  to  build  dams,  aqueducts,  etc. 


Variation  in  the  amount  of  rainfall.  There  is  a  very  great  dif- 
ference in  the  amount  of 
rainfall  in  different  sec- 
tions of  our  country.  To 
see  this,  examine  care- 
fully figure  76.  The  en- 
tire western  part  of  the 
United  States,  with  the 
exception  of  the  extreme 
northwestern  region,  has 
very  little  rainfall.  In 
most  places  less  than 
twenty  inches  a  year  falls, 
while  in  the  southwestern 
part  there  are  some  local- 
ities with  less  than  five 
inches  of  rain.  It  is  some- 
times possible  to  reclaim 
these  waste  places,  mak- 
ing them  fertile  and  beautiful,  since  the  soil  usually  contains 
exactly  what  the  plants  need  with  the  exception  that  the  water 
is  lacking.  This  recla- 
mation is  made  possible 
by  what  is  known  as 
irrigation. 

Reclaiming  desert  re- 
gions. Much  land  in 
the  western  part  of  the 
United  States  has  been 
reclaimed  by  irrigation 
projects.  Great  dams 
have  been  built  to  hold 

Up       the      Water      which  FIG.  78.  The  Roosevelt  Dam,  Salt  River  Project. 

£  .  .  The  reservoir  is  shown  full  of  water.     Such  a  dam 

COmeS    irom    the   melting  as  this  auows  the  water  supply  to  be  fed  to  the 

SnOW    On    the    mountain-  irrigated  farms  as  it  is  needed. 

sides.y  By  means  of  ca- 
nals and  ditches  this  water  is  distributed  during  the  dry  season 
to  the  fields.     This  is  what  is  known  as  irrigation. 


WATER  AND  THE  SOIL 


137 


A  great  movement  to  carry  on  this  work  was  given  a  successful  start 
during  the  administration  of  Theodore  Roosevelt.  In  his  message  to  Con- 
gress on  the  3d  of  December,  1901,  he  said  in  part:  "The  reclamation  and 
settlement  of  arid  lands  will 
enrich  every  portion  of  our 
country,  just  as  the  settle- 
ment of  the  Ohio  and  Missis- 
sippi Valleys  brought  pros- 
perity to  the  Atlantic  States." 
Shortly  after  1901  over  thirty 
Government  projects  of  this 
nature  were  undertaken,  and 
in  the  report  of  1907  it  was 
stated  that  1881  miles  of  ca- 
nals had  been  dug,  281  large 
structures  had  been  erected  FlG"  79'  A  young  orchard  under  irrigation.  Ya- 

bLlU.CLU.rt-o     lldU.     LfCCll    ClvXxLCvl)  ,  .  T*»       •  ITT      i  •  r»  £*.*£.          A.  f      -A. 

.  kima  Project,  Washington.   Some  of  the  finest  fruit 

including    some    very    large       in  the  country  comes  from  the  lava  soil  of  the 
dams,  like  the  one  shown  in       Columbia  plateau  when  its  richness  is  set  free  by 
the  illustration,  100  miles  of      irrigation, 
branch    railroads    had   been 

constructed,  and  14,000  people  had  settled  in  what  had  formerly  been  a 
desert.  This  work  has  continued.  Each  year  the  Government  under- 
takes new  irrigation  projects,  so  that  now  millions  of  acres  of  land,  once 
unprofitable,  have  been  made  useful  by  irrigation. 

Air  in  the  soil.  Although  many  people  fail  to  realize  it,  a 
necessary  part  of  the  soil  is  its  air.  If  too  much  water  fills  the 
little  pores  between  the  soil  particles,  it  drives  the  air  out.  Most 
seeds  cannot  sprout  then,  for  a  seed,  a  baby  plant,  needs  air  just 
as  a  human  baby  does.  (See  page  46.)  The  valuable  soil  bac- 
teria cannot  live  successfully  without  air.  One  reason  for  cul- 
tivating and  stirring  the  soil  frequently  is  to  admit  air  below  the 
surface. 

Reclaiming  swampy  regions.  Most  crops  will  not  grow  in 
swampy  soils  because  they  contain  too  much  water  and  too  little 
air.  In  Florida,  as  well  as  in  certain  other  sections,  large  proj- 
ects have  been  successfully  carried  out  for  the  draining  of  lands. 
Most  seeds  will  not  germinate  under  water,  since  they  need  a 
larger  amount  of  oxygen  than  can  be  absorbed  by  the  water. 
They  are  really  drowned  when  there  is  too  much  water.  Roots 
also  of  most  plants  that  we  use  as  foods  need  more  air  than  can 


138  WATER  AND  HOW  WE  USE  IT 

reach  them  if  all  the  pores  in  the  soil  are  filled  with  water.  That 
ground  through  which  water  slowly  soaks  is  the  best  for  most 
crops.  Another  reason  why  saturated  soil  is  harmful  to  the 
kinds  of  plants  that  man  cultivates  is  that  the  sun  is  not  able  to 
warm  the  earth  when  covered  by  water  nearly  as  effectively  as 
soil  that  is  properly  drained.  Draining  swamps,  therefore,  adds 
to  the  productive  areas  of  the  country  by  giving  the  land  a 
chance  to  get  the  necessary  air  and  warmth. 

Acid  soil  and  how  to  correct  it.  Why  do  crops  sometimes  fail 
to  grow  well?  One  reason  may  be  that  the  soil  is  "sour";  that 
is,  it  contains  acid.  There  are  millions  of  acres  of  acid  soil  in  the 
United  States.  Some  signs  of  it  are  the  presence  of  a  mossy 
growth  on  the  surface,  and  an  abundant  growth  of  the  weed, 
"  sorrel."  You  may  be  sure  whether  the  soil  in  your  garden  is 
acid  or  not  by  trying  the  test  described  in  the  problem  on 
page  124. 

The  cause  for  soil  acidity  is  the  action  of  bacteria.  When  they 
attack  the  waste  matter  in  the  soil  (see  page  132)  they  give  off 
certain  acids.  In  "  sweet  "  soil  these  acids  immediately  unite 
with  other  materials,  but  if  the  necessary  materials  are  lacking, 
the  acids  collect.  One  substance  which  unites  readily  with  acids 
is  lime,  so  the  best  way  to  correct  acid  soil  is  to  work  lime  well 
into  it. 

INDIVIDUAL  PROJECTS 

Working  projects: 

1.  Make  a  collection  of  rocks  and  minerals  found  in  your  locality.     Try  to 
find  out  the  name  of  each.     Label  them  and  arrange  them  in  a  cabinet. 

2.  Prepare  the  soil  for  your  garden.     It  must  be  ploughed  or  dug,  harrowed 
or  spaded  thoroughly,  and  enriched.     The  books  on  gardening  listed  on 
page  162  will  help  you. 

3.  Test  for  acidity  various   household    materials,  such  as  soda,  cream  of 
tartar,  salt,  etc.     Report  your  results  to  the  class. 

Reports: 

1.  The  story  of  the  Great  Glacier. 

After  reading  such  an  account  as  is  found  in  Rogers's  Earth  and  Sky,  or 
Winslow's  The  United  States,  make  the  most  vivid  report  that  you  are  able. 

2.  The  story  of  how  coal  was  made. 

Collect  specimens  of  different  kinds  of  coal  to  show  the  class.  Tell  the 
story  which  one  of  those  pieces  could  tell  if  it  were  able  to  relate  its 
experiences.  See  the  account  in  Wonders  of  Science. 


WATER  AND  THE  SOIL  139 

3.  Diamonds  and  diamond  mines. 

Explain  the  chemical  relation  between  coal  and  diamonds.  From  such 
an  account  as  is  found  in  Carpenter's  Africa  describe  to  the  class  how  dia- 
monds are  found  in  the  earth's  crust  and  mined. 

4.  Great  caves;  their  causes  and  characteristics. 

If  you  have  ever  been  in  a  great  cave,  tell  your  experiences  and  impres- 
sions. Collect  pictures  of  caves.  Read  Rogers's  description  of  the  Mam- 
moth Cave,  or  Professor  Shaler's  account  in  Wonders  of  Science. 

5.  Active  volcanoes  of  the  world. 

Find  out  from  geographies  where  active  volcanoes  are  located.  Show 
pictures  of  eruptions  and  the  destruction  wrought  by  them. 

6.  The  story  of  gold. 

See  reference  below.  • 

7.  Reclaiming  the  desert. 

See  Chamberlain's  North  America  for  an  account  of  how  irrigation  trans- 
forms a  desert.  Pictures  may  be  shown  to  make  your  report  more  inter- 
esting. 

For  other  suggestions  see  the  list  of  references. 

BOOKS  THAT  WILL  HELP  YOU 

Africa.     F.  G.  Carpenter.     American  Book  Co. 

Contains  a  description  of  Kimberley  and  the  diamond  mines. 
Diggers  in  the  Earth.     E.  M.  Tappan.     Houghton  Mifflin  Co. 

In  a  coal  mine. 
Earth  and  Sky  Every  Child  Should  Know.   J.  E.  Rogers.    Doubleday,  Page  &  Co. 

'The  Work  of  the  Wind." 
What  Becomes  of  the  Rain." 
How  Rocks  are  Made." 

'The  Great  Ice-Sheet." 

'The  Mammoth  Cave." 

'How  Coal  was  Made." 
North  America.     J.  F.  and  A.  H.  Chamberlain.  The  Macmillan  Co. 

Reclaiming  the  desert. 

The  Story  of  Agriculture  in  the  United  States.     A.  H.  Sanford.     D.  C.  Heath 
&  Co. 

Irrigation  and  dry  farming. 

The  Story  of  Gold.     E.  S.  Meade.     D.  Appleton  &  Co. 
The  United  States.     I.  O.  Winslow.     D.  C.  Heath  &  Co. 

Coal. 

The  Great  Glacier  and  its  Effects. 
The  Wonder  Book  of  Volcanoes  and  Earthquakes.     E.  J.  Houston.     Fred.  A. 

Stokes  Co. 
Wonders  of  Science.     E.  M.  Tappan,  Editor.     Houghton  Mifflin  Co. 

'A  Moving  Picture  of  the  Story  of  the  Earth."     (Gibson.) 

'How  Soil  is  Made."     (Shaler.) 

'The  Work  of  Mud."     (Winchell.) 

'About  Pebbles."     (Kingsley.) 

'  How  Caves  are  Made."    (Shaler.) 

'The  Autobiography  of  a  Piece  of  Coal."     (Taylor.) 
U.S.  Department  of  Agriculture,  Farmers'  Bulletin  864.     Irrigation. 

Magazine  articles: 

"Making  the  Desert  Bloom."     Blanchard.     Scientific  American,  March  4, 
1916. 


140  WATER  AND  HOW  WE  USE  IT 

"Notes  on  the  History  of  Coal  in  the  United  States."  Scientific  American 
Supplement,  March  4,  1916. 

"The  Precious  Stones  Industry  in  the  United  States."  Scientific  American 
Supplement,  March  25,  1916. 

"Some  American  Glaciers."  Ellis.  Scientific  American  Supplement,  April 
29,  1916. 

"Wood  Older  than  the  Hills."  Scientific  American  Supplement,  March  4, 
1916. 


UNIT  III 
FOODS  AND  HOW  WE  USE  THEM 


PROJECT  VIII 
PLANTS  —  FOOD-MAKERS  FOR  THE  WORLD 

Foods  —  a  necessity  of  life.  Our  previous  projects  have  re- 
lated to  certain  necessities  of  life,  —  namely,  air  and  water.  There 
is  a  great  abundance  of  both  of  these  things  upon  the  earth.  The 
air  is  free  to  all  and  drinking-water  is  cheap.  On  the  other  hand, 
food,  a  third  great  necessity  of  life,  is  an  expensive  commodity. 
For  many  reasons  it  is  destined  to  become  even  more  expensive 
in  the  future.  The  tendency  to  abandon  the  farm  for  the  city  and 
the  decreasing  fertility  of 
the  soil  have  been  among 
the  most  important  causes 
of  rising  prices.  Nowa- 
days we  hear  much  about 
the  work  of  the  farmer. 
Back-yard  gardens  are 
becoming  popular.  Man 
has  been  forced  in  recent 
years  to  study  much  more 
thoroughly  than  ever  be- 
fore the  conditions  that 
are  favorable  for  food- 
making.  The  Department 
of  Agriculture  at  Wash-  FlG  8o  A  back.yard  garden. 

ington   as   well   as   many 

State  departments  are  actively  engaged  in  helping  the  people  of 
the  country  to  produce  food.  Recently  millions  of  dollars  have 
been  appropriated  by  the  Federal  Government  to  help  establish 


142 


FOODS  AND  HOW  WE  USE  THEM 


agricultural  stations  and  colleges,  and  rural  high  schools  are 
beginning  to  see  the  importance  of  having  courses  in  agriculture. 
People  who  live  in  cities  as  well  as  those  who  earn  their  living 
by  tilling  the  soil  have  come  to  realize  that  their  welfare,  that 
indeed  their  very  existence,  is  dependent  upon  the  successful 
work  of  the  farmer. 

Food  conservation.  During  the  Great  War  much  was  accom- 
plished in  the  line  of  saving  food.  Food  conservation  is  a  neces- 
sity of  peace  as  well  as  of  war.  You  may  continue  to  render 
patriotic  service  by  helping  raise  more  food.  Perhaps  groups 
in  your  class  may  wish  to  form  clubs,  as  suggested  on  page  161. 
You  will  find  the  State  and  Federal  Governments  ready  to  help 
you  in  many  ways.  Organizations  like  the  Scouts  and  Camp- 
Fire  Girls  have  done  and  are  doing  much  to  help  in  food  produc- 
tion and  conservation.  Do  your  part. 

PROBLEM  i :  WHAT  ARE  THE  SOURCES  OF  OUR  FOODS? 

Directions: 

Arrange  a  table  with  three  columns : 


ANIMAL  FOODS 

VEGETABLE  FOODS 

MINERAL  FOODS 

In  the  first  column  write  the  names  of  kinds  of  food  which  come  from 
animals.  In  the  second  column  write  the  names  of  foods  which  come  from 
plants,  including  roots,  leaves,  fruits,  and  any  other  parts.  In  the  third 
column  write  the  names  of  any  foods  which  come  from  neither  animals  nor 
plants. 

Summary: 

From  what  source  do  most  of  our  foods  come? 

Questions: 

1.  Where  do  animals  get  their  food? 

2.  What  is  the  greatest  source  of  food? 


PLANTS  143 

PROBLEM  2 :  OF  WHAT  DO  FOODS  CONSIST? 

Directions: 

Study  the  charts  issued  by  the  United  States  Department  of  Agriculture 
on  Composition  of  Food  Materials.  (See  pages  174-178.) 

What  does  the  shading  mean?  (We  may  call  each  of  the  substances  rep- 
resented a  nutrient  or  food  unit.) 

How  many  nutrients  may  be  present  in  a  food? 

Make  a  list  of  a  number  of  foods  which  contain  a  large  percentage  of 
protein,  in  each  case  stating  the  percentage. 

Make  other  lists  of  foods  which  contain  large  percentages  each  of  fat, 
carbohydrates,  ash,  or  mineral  matter,  and  water,  stating  the  percentages 
in  each  case. 

Summary: 

1.  Which  food  in  your  lists  contains  the  largest  percentage  of  protein? 
Which  contains  the  largest  percentage  of  fat?  of  carbohydrate?  of  ash? 
of  water? 

2.  In  general,  do  animal  or  vegetable  foods  furnish  more  protein?  more 
fat?  more  carbohydrate?  more  ash?  more  water? 

PROBLEM  3 :  To  TEST  SEEDS  FOR  PROTEIN. 

Directions: 

Part  i.     What  is  the  test  for  protein? 

In  four  test-tubes  place  egg-white,  sugar,  salt,  and  cornstarch. 

Into  each  test-tube  pour  a  little  dilute  nitric  acid  (caution!),  heat  gently, 
and  watch  results. 

Which  food  changes  most? 

Now  add  to  the  mixtures  in  the  test-tubes  a  little  dilute  ammonium 
hydroxide. 

Which  food  changes  most?    What  color  results? 

Find  out  from  the  food  charts  what  nutrient,  aside  from  water,  is  most 
abundant  in  egg-white. 

Describe  the  test  for  protein. 

Part  2.  Testing  seeds. 

Use  soaked  seeds,  cut  in  pieces.  Place  each  kind  of  seed  in  a  separate 
test-tube;  add  nitric  acid;  heat  gently;  and  add  ammonium  hydroxide. 

Summary: 

List  in  a  table  the  seeds  tested  by  the  class. 


144 


FOODS  AND  HOW  WE  USE  THEM 


SEEDS  CONTAINING 


Much  protein 

Little  protein 

No  protein 

.    '   • 

Question: 

Is  the  yellow  substance  protein,  or  is  it  a  new  substance  produced  by 
chemical  action? 

PROBLEM  4 :  To  TEST  SEEDS  FOR  FAT. 

Directions: 

Part  i.  What  is  the  test  for  fat? 

On  squares  of  brown  paper  place  small  amounts  of  lard,  sugar,  corn- 
starch,  salt,  and  egg-white.  Leave  them  a  few  minutes  on  a  warm  surface 
like  a  radiator  or  pan  over  a  gas-burner. 

Remove  the  food  and  examine  the  paper.  Which  food  has  made  a 
grease  spot  on  the  paper? 

Find  out  from  the  food  chart  the  nutrient  most  abundant  in  lard. 

Describe  a  test  for  fat. 

Part  2.  Testing  seeds. 

The  seeds  must  be  ground  up  fine.  Use  common  seeds  used  for  food ;  also 
nuts,  castor-oil  beans,  flaxseed,  etc. 

Place  small  heaps  of  the  ground  seeds  each  on  separate  papers;  heat 
gently;  and  look  for  grease  spots. 

Summary: 

List  the  seeds  tested  by  the  class,  as  follows: 

SEEDS  CONTAINING 


Much  fat 


Little  fat 


No  fat 


PLANTS 

PROBLEM  5 :  To  TEST  SEEDS  FOR  STARCH. 

(Note:  Two  common  carbohydrates  in  food  are  starch  and  sugar.) 


145 


Directions: 

Part  i.  What  is  the  test  for  starch? 

In  one  test-tube  place  a  little  cornstarch;  in  other  test-tubes  about  the 
same  amount  of  sugar,  salt,  lard,  and  egg-white. 

Into  each  tube  drop  a  little  iodine  solution.     What  is  its  color? 

Watch  and  describe  the  effect  on  the  substances  in  the  tubes. 

Why  is  iodine  used  as  a  test  for  starch? 

Part  2.  Testing  seeds. 

Use  seeds  which  have  been  soaking  over  night.  Large  seeds,  such  as 
kidney  beans,  lima  beans,  castor-oil  beans,  peas,  corn  kernels,  etc.,  are  best. 

Cut  open  the  seeds  to  be  tested.  Place  them  in  a  small  dish  and  drop  a 
little  iodine  upon  each  seed. 

Watch  the  effects  for  some  minutes. 

Summary: 

Show  in  a  table  the  results  obtained  by  the  class. 

SEEDS  CONTAINING 


Much  starch    ' 

Little  starch 

No  starch 

0 

Question: 

Is  the  purple  substance  starch? 

PROBLEM  6:  To  TEST  SEEDS  FOR  SUGAR. 

Directions: 

Part  i.  What  is  a  test  for  sugar? 

Place  small  amounts  of  sugar,  salt,  cornstarch,  egg-white,  and  lard  in 
test-tubes.  Add  a  little  Fehlings'  solution,  which  can  be  bought  from  a 
drug-store.  Heat  gently.  Observe  all  changes  until  the  substances  have 
each  boiled  two  minutes.  Allow  the  test-tubes  to  stand  a  few  minutes. 

In  which  tube  do  you  find  a  brick-red  powder? 

Describe  the  test  for  sugar. 


146 


FOODS  AND  HOW  WE  USE  THEM 


Part  2.  Testing  seeds. 

Grind  up  the  seeds  to  be  tested,  and  place  them  in  separate  test-tubes. 
Add  Fehlings'  solution  and  boil.     Watch  for  the  orange  or  brick-red  color. 

Summary: 
List  the  seeds  tested  by  the  class  in  a  table. 

SEEDS  CONTAINING 


Much  sugar 

Little  sugar 

No  sugar 

Question: 

Is  the  brick-red  powder  sugar? 

PROBLEM  7:  To  TEST  SEEDS  FOR  ASH  OR  MINERAL  MATTER. 
Directions: 

Part  I.  What  is  the  test  for  ash? 

Place  small  amounts  of  salt,  lard,  sugar,  and  cornstarch  on  squares  of 
asbestos  sheeting.  Try  to  burn  up  each  substance  with  a  Bunsen  flame. 
(Caution!) 

Which  food  refuses  to  burn? 

Find  out  from  the  charts  the  amount  of  ash  in  each  of  these  foods. 

What  is  the  color  of  ash  left  from  burning  wood,  paper,  etc? 

Describe  the  test  for  ash  or  mineral  matter. 

Part  2.  Testing  seeds. 

Use  seeds  ground  up  fine.  Burn  each  kind  on  a  separate  piece  of  as- 
bestos sheeting.  Look  for  white  ash. 

Summary: 

List  the  seeds  tested  in  a  table. 


SEEDS  CONTAINING 


Much  ash 

Little  ash 

No  ash 

PLANTS  147 

PROBLEM  8 :  To  TEST  SEEDS  FOR  WATER. 

Directions: 

Part  i.  What  is  a  test  for  water? 

Place  a  small  amount  of  water  in  a  test-tube.  Heat  it.  What  appears 
on  the  sides  of  the  tube?  Into  what  does  the  water  change? 

If  water  is  present  in  anything  which  is  heated,  what  happens  to  the 
water? 

How  can  this  test  be  used  to  detect  water  which  does  not  show? 

Part  2.  Testing  seeds. 

Use  dry  seeds  of  different  kinds.  Cut  or  grind,  and  place  each  kind  in  a 
separate  test-tube.  Heat,  being  careful  not  to  char  the  seeds. 

Summary: 

List  the  seeds  tested  by  the  class  in  a  table. 

SEEDS  CONTAINING 


Much  water 

Little  water 

No  water 

PROBLEM  9:  WHAT  ARE  THE  USES  OF  EACH  PART  OF  A  PLANT? 

Directions: 

Pull  up  a  weed  while  in  flower.  Wash  off  the  soil  and  place  the  roots 
in  a  glass  of  water  colored  with  red  ink.  Locate  the  organs  of  the  plant  — 
the  roots,  the  stem,  the  leaves,  the  flower. 

Uses  of  roots. 

Dig  up  two  similar  plants.  Place  the  roots  of  one  plant  in  water,  and 
the  roots  of  the  other  in  an  "empty"  glass.  Which  withers  first?  Why? 
What  use  of  roots  have  you  shown? 

Carefully  dig  the  soil  away  from  the  roots  of  a  plant,  exposing  the  roots. 
How  are  they  arranged?  When  all  the  soil  is  removed,  what  happens  to 
the  plant?  What  use  of  roots  have  you  shown? 

Let  certain  members  of  the  class  test  roots  such  as  carrot,  parsnip,  etc., 
for  nutrients.  What  use  of  roots  is  thus  shown? 

Uses  of  stems. 

Find  a  "stemless"  plant  like  dandelion,  mullein,  plantain,  etc.  Con- 
trast the  arrangement  of  leaves  on  this  plant  with  the  weed  you  are  study- 


148 


FOODS  AND  HOW  WE  USE  THEM 


ing.  Contrast  with  such  plants  as  ivy,  woodbine,  or  pole  beans.  What 
use  of  the  stem  have  you  discovered? 

Cut  across  the  stem  of  your  weed,  which  has  been  in  colored  water, 
about  an  inch  above  the  level  of  the  water.  Does  this  show  you  another 
use  of  stems? 

Let  certain  members  of  the  class  test  stems  such  as  potato,  onion,  and 
asparagus  for  nutrients.  What  use  of  stems  is  thus  shown? 

Uses  of  leaves. 

Make  an  apparatus  as  shown  in  the  sketch  on  page  98,  using  two  glasses, 
a  punched  card,  and  a  leaf.  The  stem  of  the  leaf  must  be  in  water.  Set  the 
apparatus  in  the  sun.  What  appears  on  the  sides  of  the  glass?  What  use 
of  leaves  is  thus  shown? 

Examine  a  thin  piece  of  the  skin  of  a  leaf  with  the  compound  microscope. 
Find  the  breathing  pores  in  the  skin.  What  use  of  leaves  does  the  presence 
of  these  pores  suggest? 

Let  certain  members  of  the  class  test  leaves,  such  as  cabbage,  lettuce, 
spinach,  etc.,  for  nutrients.  What  do  the  results  indicate? 

Use  of  flowers. 

Are  any  of  the  flowers  on  your  weed  going  to  seed? 

What  are  seeds  for?  What  is  the  use 
of  the  flower? 

Summary: 

Sum  up  what  you  have  learned  about 
the  uses  of  each  organ  of  a  plant. 

PROBLEM  10:  WHERE  is  STARCH  MADE  IN 
A  PLANT? 

Directions: 

Cut  a  cork  stopper  in  two,  and  fasten 
the  two  halves  upon  a  leaf  of  a  growing 
geranium  plant.  (See  diagram.)  Place  the 
geranium  in  bright  sunlight  about  twenty 
minutes.  Then  pick  off  the  leaf  and  re- 
move the  cork. 

Is  the  appearance  of  the  leaf  changed? 
To  find  out  if  it  contains  starch  we  must 
bleach  the  leaf,  since  the  green  color  hides 
any  color  change.  To  do  this,  boil  the  leaf 
in  water  one  minute,  then  plunge  it  into 
alcohol  and  shake.     What  happens  to  the  alcohol?   To  the  leaf? 

When  the  leaf  is  bleached  as  much  as  possible,  rinse  with  clear  water, 
and  dip  into  iodine. 

Is  starch  present?     If  so,  where? 


81 


Finding  out  if  starch  is 
made  in  leaves. 


PLANTS  149 

Bleach  and  test  a  striped  green  and  white  leaf  which  has  been  in  bright 
sunlight  twenty  minutes.     Is  starch  present?     If  so,  where? 
Conclusions: 

Does  starch  appear  where  there  is  no  green  color? 

Does  starch  appear  where  the  sunlight  cannot  reach  the  leaf? 
Questions: 

1.  What  do  you  infer  as  to  where  starch  is  made  in  a  plant? 

2.  Can  mushrooms  make  starch?     Explain. 

PROBLEM  1 1 :  How  DOES  THE  LEAF  GET  WATER  FOR  STARCH-MAKING? 

Directions: 

Place  a  bunch  of  celery  in  a  glass  of  water  colored  with  red  ink.  Observe 
from  time  to  time.  What  happens? 

Cut  across  the  stalks.     Can  you  see  the  bundles  of  water-pipes  or  ducts  ? 

Examine  the  structure  of  the  leaves.  Through  what  does  the  water 
pass? 

Summary: 
Trace  the  pathway  which  water  follows  from  roots  to  leaves. 

Question: 
How  could  you  prepare  green  carnations  for  St.  Patrick's  Day? 

PROBLEM  12:  How  ARE  ROOTS  FITTED  TO  TAKE  IN  WATER  FROM  THE  SOIL? 

Directions: 

Cut  a  circle  of  colored  blotting-paper  to  fit  a  small  round  dish,  such  as  a 
Syracuse  watch  glass  or  a  butter  plate.  Moisten  it  thoroughly.  Place  a 
few  radish  seeds  on  the  moist  paper.  Cover  with  a  glass  and  set  aside. 
Observe  from  day  to  day. 

What  is  the  first  thing  to  sprout  from  the  seed? 

How  soon  do  the  roots  show  any  fuzzy  white  root-hairs  ? 

On  what  part  of  the  roots  do  the  root-hairs  appear? 

Do  root-hairs  increase  or  decrease  the  absorbing  surface  of  roots? 

PROBLEM  13:  To  MAKE  AN  ARTIFICIAL  ROOT-HAIR. 

(Note  —  Root-hairs  are  so  small  that  it  is  difficult  to  see  how  they 
work.  We  can  make  an  artificial  root-hair  large  enough  to  see  by  using 
an  egg  and  some  glass  tubing.) 

Directions: 

With  sealing-wax  fasten  a  piece  of  glass  tubing  about  six  inches  long  to 
the  small  end  of  a  fresh  egg.  Be  sure  that  the  sealing  wax  allows  no  chance 
for  a  leak.  When  it  is  cool  carefully  punch  a  hole  in  the  eggshell  by  pushing 
a  hat  pin  or  knitting-needle  through  the  tube.  Now  very  carefully  chip  off 


150 


FOODS  AND  HOW  WE  USE  THEM 


some  of  the  eggshell  at  the  other  end  of  the  egg,  taking  care  not  to  break 
the  inner  membrane.  With  a  short  piece  of  rubber  tubing  fasten  a  long 
piece  of  glass  tubing  to  the  piece  already  attached 
to  the  egg.  Set  the  egg  in  water,  and  support 
the  tubing  firmly. 

The  apparatus  represents  a  root-hair,  which 
is  really  one  plant  cell.  What  represents  the  cell 
wall?  The  cell  sap  inside  the  cell?  The  soil 
water  outside  the  cell? 

Watch  the  tube  for  some  time.  Set  the  appa- 
ratus away  for  several  days,  and  observe  each 
day. 

Summary: 

Explain  how  this  experiment  helps  you  to 
understand  the  work  of  root-hairs. 

Question: 

How  many  ways  can  you  suggest  in  which 
this  artificial  root-hair  differs  from  a  real  root- 
hair? 

PROBLEM  14:  How  ARE  LEAVES  FITTED  TO  GET 
CARBON  DIOXIDE  FOR  STARCH-MAKING? 

Directions: 

Part  I.  Does  the  air  contain  carbon  dioxide? 
(See  problem  4,  page  24.) 

Part  2.  How  can  the  air  get  into  a  leaf?  (See 
problem  1 1 ,  page  38.) 

Summary: 

Where  does  a  leaf  get  carbon  dioxide?     Ex- 
FIG.  82.  An  artificial  P^am  now  a*r  can  Set  in  and  out  through  the 

root-hair.  epidermis  of  a  leaf. 

PROBLEM  15:  To  OBTAIN  A  LIBRARY  OF  GARDEN  INFORMATION. 

Directions: 

The  Federal  Government  and  some  of  the  State  Governments  publish 
bulletins  and  circulars  which  can  be  of  great  assistance  to  you.  Form  the 
"bulletin  habit."  Send  for  bulletins;  then  when  you  receive  them,  read 
them  and  use  the  information. 

When  writing  for  bulletins  published  by  the  National  Government,  send 
to  your  Congressman,  or  to  the 

Chief  of  the  Division  of  Publications, 

United  States  Department  of  Agriculture, 
Washington,  D.C. 


PLANTS 


Seed-growers    and    dealers  in  agricultural   machinery  often  publish 
pamphlets  of  great  value  which  you  may  be  able  to  obtain. 

Summary: 

Make  a  list  of  the  books  and  pamphlets  in  your  garden  library. 

PROBLEM  16:  To  PLAN  MY  HOME  GARDEN. 

Directions: 

With  a  yardstick  or  tape  measure  carefully  measure  the  plot  which  you 
are  to  use. 

Drive  a  stake  in  each  corner. 


APRIL 


MAV 


JUNE 


JULY       AUG. 


FIG.  83.  A  vegetable  garden  plan,  showing  currants  to  divide  garden  from  yard.  By  con- 
tinuing hedge  around  garden  you  can  enclose  entire  garden.  Asparagus,  rhubarb,  and  horse- 
radish are  permanent  growers,  shown  planted  on  one  side  of  walk  where  these  beds  will  not 
be  disturbed. 

The  hotbed  and  compost  pile  are  also  permanent  features  of  a  successful  garden.  This  plan 
shows  a  strip  4^  feet  wide,  running  full  length  of  garden,  and  2%  feet  for  walk. 

The  divisions  by  months  indicate  what  varieties  should  be  planted  during  the  month,  and 
the  flower  border  is  for  decorative  purposes. 

(Courtesy,  International  Harvester  Co.) 


Make  a  plan  on  paper,  using  a  scale.  For  example  let  one-half  inch  rep- 
resent one  foot.  Be  sure  that  the  shape  of  your  garden  is  correctly  drawn. 
Mark  the  north  with  the  letter  "N." 

After  a  study  of  the  circulars,  or  consultation  with  older  people  who  can 
give  practical  advice,  decide  just  what  vegetables  you  will  raise.  Do  not 
try  too  many  kinds. 

Plan  the  arrangement  of  the  rows.  Early  crops  may  be  planted  between 
the  rows  of  late  crops.  Be  sure  that  the  rows  are  the  correct  distance  apart. 


152         FOODS  AND  HOW  WE  USE  tHEM 

Show  on  your  plan  the  location  of  the  rows.  Make  two  copies  of  the 
plan,  one  to  take  to  the  garden  with  you,  and  one  to  preserve  for  your 
notebook. 

PROBLEM  17:  To  MAKE  AND  USE  A  SEED  TESTER. 

Directions: 

Use  two  table  plates.  Cut  two  pieces  of  cotton  flannel  or  other  thick 
cloth  to  cover  the  bottoms  of  the  plates. 

Boil  the  cloths  five  minutes.  What  effect  does  the  boiling  have  on  any 
bacteria  or  mold  spores  that  may  be  on  the  cloth? 

Wring  out  the  cloths;  spread  one  on  a  plate;  and  put  one  hundred  small 
seeds  of  the  same  kind  upon  it.  Cover  these  with  the  other  cloth.  Place 
the  second  plate  over  the  one  containing  the  seeds,  with  the  rims  together. 
Set  the  tester  in  a  warm  place. 

Look  each  day  to  see  if  the  seeds  germinate  or  sprout.  Remove  with 
a  forceps  those  that  germinate.  When  all  have  germinated  that  will, 
subtract  the  number  that  failed  to  germinate  from  one  hundred. 

Summary: 

1.  What  per  cent  of  the  seeds  tested  germinated? 

2.  What  is  the  use  of  testing  seed  before  purchasing?   before  planting? 

Where  our  foods  come  from.  Have  you  ever  considered  where 
your  food  comes  from  ?  The  country  boy  knows.  He  probably 
helps  to  raise  the  crops  that  make  up  a  large  part  of  his  food- 
supply,  and  he  helps  feed  the  live-stock  of  the  farm  and  drive 
them  to  the  place  where  they,  too,  become  a  part  of  the  food-sup- 
ply for  human  beings.  City  boys  and  girls  sometimes  fail  to 
realize  where  the  food  comes  from  before  it  reaches  the  market 
where  they  buy  it. 

All  food  can  be  classified  as  animal,  vegetable,  and  mineral  food. 
Most  of  us  eat  all  three  kinds,  yet  there  is  a  large  part  of  the  pop- 
ulation of  the  world,  especially  in  the  crowded  countries  like 
India  and  China,  who  eat  little  animal  food.  Animals,  indeed, 
get  their  food  from  plants,  so  when  we  eat  meat  we  are  going 
back,  in  an  indirect  way,  to  plants  for  our  food  supply. 

Organic  and  inorganic  foods.  All  foods  may  be  grouped  in  an- 
other way  in  two  classes.  They  are  either  organic  or  inorganic. 
Organic  foods  come  from  living  things,  plants  or  animals.  Inor- 
ganic foods  come  from  non-living  things.  The  terms  organic  and 
inorganic  may  be  applied  not  simply  to  foods,  but  to  any  sub- 


PLANTS  153 

stances  when  one  wishes  to  designate  their  origin.  For  exam- 
ple, such  things  as  wood  and  clothing  are  organic  because  they 
come  direct  either  from  plants  or  animals,  while  materials  like 
iron,  silver,  gold,  etc.,  are  inorganic. 

Almost  all  foods  are  obtained  from  living  things.  Thus,  from 
animals,  for  example,  we  obtain  meat,  fish,  butter,  eggs,  milk  and 
cream ;  while  from  plants  we  get  such  things  as  cereals,  vegetables, 
and  fruits.  These  are  organic  foods.  The  inorganic  foods  are 
of  two  kinds:  water  and  salts,  or  mineral  matter.  Common  table 
salt  is  perhaps  the  most  familiar  example  of  mineral  matter. 

There  is  another  important  difference  between  organic  and  in- 
organic foods.  Organic  foods,  as  well  as  other  kinds  of  organic 
things,  always  contain  the  element  carbon.  Inorganic  substances 
never  contain  this  element. 

The  nutrients.  Every  article  of  food  that  we  know  anything 
about  consists  of  one  or  more  of  five  fundamental  food  substances. 
These  food  units  are  called  nutrients. 

There  are  three  organic  nutrients  and  two  inorganic  nutrients. 
The  organic  nutrients  are  called  protein,  carbohydrate,  and  fat. 
There  are  several  kinds  of  carbohydrates,  the  most  important  of 
which  are  sugar  and  starch.  The  inorganic  nutrients  are  water 
and  salt. 

Since  foods  replenish  the  materials  that  are  being  used  in  plants 
and  animals,  it  would  be  natural  to  suppose  that  foods  consist 
of  the  elements  present  in  living  things.  (See  page  46.)  The 
four  elements  found  in  greatest  amounts  in  plants  and  animals 
are  carbon,  oxygen,  hydrogen,  and  nitrogen.  These  four  elements 
are  also  given  off  in  the  materials  which  come  from  the  living 
things  as  wastes.  Therefore  they  must  be  supplied  to.  them  to 
make  good  this  loss. 

Physical  and  chemical  changes.  The  processes  by  which  the 
nutrients  are  made  from  substances  quite  unlike  them  are  ex- 
amples of  chemical  changes.  A  chemical  change  is  one  by  which 
elements  are  rearranged  to'  produce  a  new  substance.  Chemical 
changes  are  going  on  all  around  us  every  day.  Oxidation  (see 
page  30)  is  one  of  the  commonest  examples.  Whether  the  oxi- 
dation is  rapid  enough  to  cause  a  flame  or  slow,  as  in  the  cells  of 


154         FOODS  AND  HOW  WE  USE  THEM 

the  body,  the  changes  which  are  produced  result  in  the  forma- 
tion of  new  substances. 

Other  changes  are  constantly  taking  place  which  do  not  result 
in  the  formation  of  any  different  substances.  Water  changes  to 
ice,  but  the  ice  can  melt  again  to  water.  The  moisture  in  the  air 
condenses  in  a  cloud  and  falls  to  the  ground  as  rain.  Such 
changes  are  called  physical  changes.  A  physical  change  is  one  by 
which  no  new  substance  is  formed. 

Where  do  plants  get  their  food?  We  have  found  that  plants 
are  the  great  source  of  food.  Do  they  take  in  their  food  from  the 
soil,  ready-made,  or  do  they  make  their  own  food? 

The  only  two  nutrients  which  the  plants  can  absorb  directly 
from  the  soil  are  water  and  mineral  matter,  the  inorganic  nutrients. 
Soil  water  is  very  different  from  rain  water  because  it  has  dis- 
solved in  it  some  of  the  mineral  matter  from  the  soil  itself.  If 
you  should  grow  two  plants,  one  in  rain  water  and  the  other  in 
soil  water,  you  would  find  that  the  plant  grown  in  soil  water 
would  live  much  longer  than  the  other.  Very  simple  plants,  like 
bacteria  and  molds,  which  consist  of  only  one  cell,  or  a  few  cells, 
absorb  the  soil  water  directly  through  the  cell  wall  into  the  cell 
itself.  The  higher  plants  are  more  complicated,  and  have  special 
parts  for  absorbing  the  soil  water.  These  parts  are  the  roots. 

The  organs  of  a  plant.  In  order  to  know  how  plants  are  fitted 
to  take  certain  nutrients  from  the  soil  and  make  others  within 
their  own  bodies,  we  must  know  something  of  their  structure. 
Plants  vary  in  structure  all  the  way  from  bacteria,  which  are 
made  of  only  one  cell,  to  huge  trees,  made  of  countless  millions 
of  cells. 

Let  us  consider  a  typical  food-making  plant,  the  corn.  It  is 
easy  to  see  that  there  are  distinct  parts  or  organs  in  the  plant.  It 
has  roots,  a  stem,  and  leaves,  which  may  be  called  the  organs  of 
growth.  It  also  has  flowers  in  the  form  of  the  tassel  and  the  ear. 
The  flowers  contain  what  are  called  the  organs  of  reproduction, 
because  they  have  in  them  parts  whose  work  is  to  produce  seeds. 

To  understand  the  food-making  in  plants  we  must  know  the 
work  of  each  of  the  organs  of  growth.  Let  us  briefly  sum  up  the 
work  of  each  organ. 


PLANTS 


155 


Roots  (i)  hold  the  plant  firmly  in  the  ground;  (2)  absorb  soil 
water ;  (3)  carry  soil  water  to  the  stem ;  and  (4)  sometimes  store 
up  food  for  the  plant  to  use  later. 

Stems  (i)  hold  the  leaves  up  to  reach  the  sunlight;   (2)  carry 
the  soil  water,  with  its  mineral  matter, 
up  to  the  leaves ;  (3)  carry  sap  back  to  the 
roots;  and  (4)  sometimes  store  up  food. 

Leaves  (i)  contain  the  breathing  pores 
by  which  plants  breathe  in  oxygen  and 
breathe  out  carbon  dioxide  and  water 
vapor,  just  as  people  do;  (2)  evaporate  the 
excess  water  after  it  has  given  up  its  min- 
eral matter;  (3)  sometimes  store  up  food; 
and  (4)  most  important  of  all,  make  the 
three  organic  nutrients,  carbohydrates,  fat, 
and  protein. 

Root-hairs.  If  you  grow  some  seedling 
so  that  you  can  watch  the  roots  'develop 
(see  problem  12),  you  find  that  the  little 
roots  seem  to  be  covered  with  a  fine  white 
fuzz.  If  you  examine  the  fuzz  with  a  mi- 
croscope, you  can  see  that  each  little  bit 
of  fuzz  is  a  tiny  projection  from  the  side 
of  the  root.  The  skin  or  epidermis  of  the  root  is  made  of  cells, 
some  of  which  have  a  tiny  extension  like  a  finger.  Each  little 
root-hair,  then,  is  not  even  the  whole  of  one  cell,  but  a  part  of  an 
epidermis  cell.  The  cell  wall  is  so  thin  that  the  soil  water  can 
soak  through  it.  The  surface  of  the  root  is  greatly  increased  by 
being  covered  with  root-hairs,  so  the  roots  can  absorb  much  more 
soil  water  than  would  be  possible  without  the  hairy  covering. 

How  a  root-hair  absorbs  soil  water.  The  root-hairs  are  so 
small  that  it  is  hard  to  see  how  they  work.  It  is  quite  easy,  how- 
ever, to  make  an  artificial  root-hair  big  enough  to  see.  Figure  82 
shows  one  made  of  an  egg  with  a  long  tube  attached  to  it.  When 
such  an  apparatus  is  put  in  water,  the  water  soaks  through  the 
thin  membrane  into  the  inside  of  the  egg,  and  pushes  some  of  the 
egg-white  up  the  tube.  It  seems  strange  that  water  should  flow 


FIG.  84.  The  organs  of  a 
plant,  —  roots,  stem,  leaves, 
and  flowers. 


156 


FOODS  AND  HOW  WE  USE  THEM 


upward  in  this  way,  for  we  always  think  it  natural  for  water  to 
flow  downwards.  We  have  already  found  one  force  strong  enough 
to  cause  water  to  creep  upwards  in  our  study  of  capillary  action. 
(See  page  134.)  Here  is  another  force  strong  enough  to  have  the 
same  effect  upon  water;  it  is  called  osmosis.  Osmosis  is  the  force 
which  causes  two  fluids  which  are  separated  by  a  membrane  to  soak 
through  the  membrane  and  mix  together. 

The  flow  will  tend  to  continue  until  the  proportionate  amounts 
of  the  different  fluids  are  equal  on  both  sides  of  the  membrane. 
In  the  egg  experiment,  dissolved  salts  flow  out  of  the  egg  at  the 
same  time  that  water  is  flowing  into  it.  Water  tends  to  flow 
into  the  egg  until  the  egg  material  is  diluted  to  the  same  extent 
as  that  of  the  material  outside  in  the  glass. 

An  understanding  of  this  egg  experi- 
ment helps  us  to  comprehend  how 
real  root-hairs  work.  Each  little  root- 
hair  is  like  a  tiny  bag,  lined  with  a 
layer  of  living  protoplasm.  In  the 
center  there  is  a  liquid,  called  cell 
sap.  When  osmosis  occurs,  fluids  pass 
through  the  cell  wall  and  the  proto- 
plasmic lining.  Water  and  certain 
dissolved  salts  are  thus  taken  in  by 
the  root-hair. 

How  water  passes  through  the 
plant.  It  is  not  enough  for  water  to 
get  into  the  root-hairs;  it  must  go  all 
over  the  living  part  of  the  plant  and 
distribute  its  mineral  matter  even  as 
far  away  as  the  leaves.  This  it  does 
by  passing  from  cell  to  cell  in  the  root 
until  a  short  distance  under  the  sur- 
face of  the  root  it  is  collected  in  very  tiny  tubes.  These  tubes 
constitute  the  lower  end  of  a  system  of  passageways,  the  upper 
ends  of  which  are  the  veins  of  the  leaves.  In  other  words,  the 
tubes  which  carry  water  and  dissolved  mineral  matter  start  at 
the  roots,  are  continued  in  stems,  and  finally  end  in  the  leaves. 


FIG.  85.  A  diagram  to  show 
how  water  passes  through  a  plant. 
Every  part  of  the  plant  is  furnished 
with  water  from  the  soil.  Notice 
the  arrows  which  represent  the  up- 
ward and  downward  motion  of 
liquid. 


PLANTS  157 

Three  reasons  may  be  given  to  explain  the  passage  of  water. 
The  first  is  osmotic  or  root  pressure.  By  this  is  meant  the  force 
or  pressure  which  is  exerted  in  the  root-hairs  which  constantly 
take  in  material  from  the  surrounding  soil.  There  is  only  one 
way  in  which  this  material  can  go.  It  is  forced  upwards.  The 
second  explanation  is  capillarity.  The  tubes  in  the  roots,  stems, 
and  leaves  are  very  tiny,  and  liquids  will  therefore  rise  in  them 
to  a  considerable  height.  The  third  explanation  is  evaporation 
of  water  from  the  leaves.  This  creates  a  suction  in  the  upper  ends 
of  the  tubes  and  draws  more  water  up  to  be  evaporated. 

Where  foods  are  manufactured.  We  have  now  traced  the  soil 
water,  with  its  valuable  mineral  nutrient,  up  to  the  leaves. 
Plant  cells  which  contain  green  coloring  matter  are  the  only 
places  where  a  plant  actually  makes  its  food.  Yet  we  eat  the 
leaves  of  very  few  plants  in  comparison  with  certain  other  parts 
of  the  plant  such  as  the  seeds,  roots,  stems,  and  buds.  After  the 
food  has  been  made  in  the  leaves  of  a  plant  it  is  carried  away 
through  tubes  in  the  leaves  and  stems  to  other  places,  where  it  is 
stored.  Roots,  stems,  and  seeds  are  the  plants'  usual  storehouses, 
where  they  keep  a  supply  of  food  for  their  own  use. 

The  raw  materials  needed.  The  leaves  are  the  plants'  fac- 
tories where  the  food  is  made.  Four  finished  products  are  turned 
out  here,  the  four  organic  nutrients.  Let  us  consider  starch  as 
a  typical  food  product.  Chemists  have  studied  starch  and  find 
that  it  can  be  written  in  chemists'  shorthand  C6HIOOS.  This 
means  that  it  is  made  up  in  the  proportion  of  six  parts  of  the 
element  carbon,  ten  parts  of  the  element  hydrogen,  and  five  parts 
of  the  element  oxygen.  In  what  forms  does  the  leaf  get  these 
three  necessary  elements? 

One  substance  which  reaches  the  leaves  is  water.  Chemists 
write  water  H2O,  showing  that  it  contains  two  parts  of  the  ele- 
ment hydrogen  and  one  part  of  the  element  oxygen.  The  only 
other  element  needed  is  carbon.  We  know  that  one  of  the  gases 
in  the  air  contains  carbon,  namely  carbon  dioxide,  CO2.  Is  the 
leaf  able  to  get  this  carbon  dioxide? 

We  have  learned  that  leaves  contain  the  breathing  pores  for  the 
plant  (see  page  38),  so  we  know  that  air  can  enter  the  leaves. 


158 


FOODS  AND  HOW  WE  USE  THEM 


The  gas  in  the  air  which  the  leaves  need  for  their  breathing  is 
oxygen,  just  as  is  the  case  with  human  breathing  (see  page  42). 
The  element  which  they  need  for  making  starch  is  carbon,  and 
this  they  are  able  to  obtain  from  the  carbon  dioxide  in  the  air. 
It  enters  the  leaf  through  the  same  pores  that  the  oxygen  enters, 
but  it  is  used  for  an  entirely  different  purpose.  Be  sure  that  you 
do  not  confuse  these  two  processes.  Oxygen  enters  through  the 
pores  of  the  leaf  to  all  the  plant  cells  and  causes  oxidation  to 
go  on.  Carbon  dioxide  enters  through  the 
pores  of  the  leaf  to  the  cells  which  contain 
green  coloring  matter  and  is  used  to  help 
make  food.  The  leaf  thus  gets  all  its  neces- 
sary elements  for  starch-making  from  water 
in  the  soil  and  from  carbon  dioxide  in  the 
air.  By  using  the  right  number  of  particles, 
it  is  able  to  cause  a  chemical  change  which 
results  in  the  formation  of  starch. 

Starch  is  made  only  in  green  plants.  We 
have  now  mentioned  the  raw  materials  that 
are  needed,  but  what  about  the  machinery  by 
means  of  which  this  process  occurs?  Starch- 
making  does  not  occur  in  leaves  which  con- 
tain no  green  coloring  matter.  If  you  exam- 
ine the  illustration  at  the  side  of  the  page, 
you  will  see  that  leaves,  like  other  living 
things,  consist  of  cells.  When  these  cells  are 
examined  under  the  microscope  it  is  found 
that  most  of  them  contain  little  green  bod- 
ies called  chloroplasts  or  chlorophyl  bodies. 
Chloro  means  green  and  phyl  means  leaf.  So 
the  word  means  leaf -green.  These  chloro- 
plasts are  little  living  particles  of  matter 
which  have  the  power,  under  certain  condi- 
tions, of  manufacturing  starch.  Just  ex- 
actly how  they  accomplish  this  nobody  knows,  but  the  fact 
that  it  is  done  can  be  demonstrated  by  an  experiment;  and  the 
fact  that  it  is  not  done  when  these  green  bodies  are  absent 


-W 


FIG.  86.  A  cell  from  a 
green  leaf.  A  mass  of  liv- 
ing, moving  protoplasm. 
P,  contains  a  part  that 
is  easily  stained  and  has 
an  important  part  in  re- 
production called  the 
nucleus,  N;  tiny  green 
bodies  float  in  the  proto- 
plasm, chlorophyl  grains, 
C.  The  cell  is  surrounded 
by  a  woody  wall,  W. 


PLANTS  159 

can  also  be  proved  by  an  experiment.  (See  problem  10,  page 
148.) 

The  sun  furnishes  the  necessary  energy.  The  chloroplasts  are 
like  machinery  in  that  they  need  power  to  make  them  work.  It 
has  been  found  that  they  can  work  only  in  the  presence  of  light. 
The  sun  furnishes  the  power  with  which  these  green  bodies  manu- 
facture starch.  Since  all  food-making  is  dependent  upon  this 
process  going  on  in  the  green  cells,  the  absolutely  essential  part 
which  the  sunshine  plays  is  evident. 

The  waste  product  is  oxygen.  Most  factories  have  some  waste 
product.  In  a  starch  factory  in  the  leaf  the  waste  product  is  oxy- 
gen. When  it  uses  the  carbon  from  the  gas,  carbon  dioxide,  it 
separates  it  from  the  oxygen  which  is  also  present  in  the  compound 
and  sets  free  the  oxygen  as  an  unnecessary,  or  waste  product. 
The  oxygen  is  able  to  pass  out  of  the  pores  in  the  leaf  to  the  air. 
Food -making  by  plants  is  useful,  then,  for  two  reasons.  It  sup- 
plies the  world  with  food,  and  it  supplies  the  air  with  oxygen, 
without  which  no  life  can  exist. 

Leaves  make  all  the  organic  nutrients.  We  have  seen  how 
starch  is  made.  Fats  and  sugars  consist  of  the  same  three  ele- 
ments, carbon,  hydrogen,  and  oxygen.  They  are  made  from  the 
same  raw  materials. 

Protein,  however,  contains  other  elements  in  addition  to  these 
three,  especially  nitrogen,  sulphur,  potassium,  magnesium,  and 
iron.  These  elements  are  all  present  in  the  mineral  matter  in 
fertile  soil,  and  pass  into  the  root-hairs  of  plants  and  up  to  the 
food  factory  in  the  leaves.  The  process  by  which  they  are  made 
into  protein  is  a  very  complicated  one,  so  difficult  to  understand 
that  we  shall  not  include  it  in  this  course. 

Although  nearly  all  plants  contain  some  protein,  we  are  accus- 
tomed to  obtain  the  bulk  of  our  supply  from  animal  foods.  Meat, 
fish,  milk,  eggs,  and  cheese  are  common  foods  which  are  rich  in 
protein. 

Helping  plants  make  foods.  Land  which  has  been  used  for  many 
years  for  raising  crops  is  not  as  fertile  as  it  was  at  first,  unless 
special  steps  are  taken  to  keep  it  so.  This  is  reasonable  when  we 
consider  that  plants  are  continually  drawing  certain  essential  sub- 


160          FOODS  AND  HOW  WE  USE  THEM 

stances  from  the  soil.  The  commonest  method  of  making  good 
this  loss  of  material  from  the  soil  is  to  add  a  "  fertilizer."  The 
most  valuable  fertilizers  contain  nitrates,  and  furnish  the  nitro- 
gen necessary  for  the  making  of  protein. 

Enriching  the  soil  by  means  of  manure,  an  animal  waste,  is 
perhaps  the  most  extensively  used  method  of  fertilizing  it.  In 
the  manure  there  are  substances  which  upon  undergoing  certain 
chemical  changes  become  nitrates  and  in  this  form  are  used  by 
plants.  It  is  interesting  to  note  that  these  changes  are  brought 
about  principally  by  the  action  of  certain  bacteria.  (See  page 
88.) 

Nitrogen-fixing  bacteria.  The  nitrogen-fixing  bacteria  alone 
of  all  living  things  are  able  to  make  use  of  the  nitrogen  that  is 
present  in  the  air.  They  are  said  to  fix  or  tie  up  this  nitrogen  with 
certain  other  elements  to  form  nitrates  which  are  then  used  by  the 
plants  in  which  they  live.  These  bacteria  are  known  to  live  only 
in  a  certain  group  of  plants  called  the  legumes,  of  which  peas, 
beans,  clover,  and  alfalfa  are  the  most  common  examples. 

For  hundreds  of  years  it  has  been  noticed  that  the  soil  may 
be  enriched  by  growing  legumes  alternately  with  other  crops. 
It  was  known  that  for  some  reason  a  patch  of  ground  where,  for 
example,  beans  had  been  growing,  would  be  enriched  by  ploughing 
up  the  soil  containing  roots  of  the  bean  plants.  Even  the  an- 
cient Romans  used  to  "  rotate  their  crops,"  as  this  alternation  of 
crops  is  called.  In  other  words,  they  would  not  grow  the  same 
kind  of  crops  upon  the  same  field  year  after  year,  but  would  alter- 
nate their  crops  in  the  manner  just  indicated.  Of  course  they 
knew  nothing  about  the  reason  why  rotating  the  crops  benefited 
the  soil.  They  knew  nothing  about  the  nitrogen-fixing  bacteria, 
because  at  that  time  there  were  no  microscopes.  Now,  however, 
.it  is  possible  to  see  these  organisms,  and  also  to  test  just  how 
much  nitrogen  is  taken  out  of  the  air  when  these  bacteria  are 
present  in  a  field.  Many  scientific  experiments  of  this  kind  have 
been  performed.  We  now  know  that  the  roots  of  the  legumes 
when  ploughed  under  and  allowed  to  decay  in  the  ground  give  to 
that  soil  a  certain  amount  of  usable  nitrogen  that  a  short  time 
before  was  in  the  air  in  a  form  which  green  plants  could  not  use. 


PLANTS  161 

Electricity  as  a  means  of  taking  nitrogen  out  of  the  air.  Just  how  the 
nitrogen-fixing  bacteria  are  able  to  take  the  nitrogen  out  of  the  air  nobody 
understands.  Scientists  have,  however,  discovered  a  means  of  taking  ni- 
trogen out  of  the  air  and  fixing  it  by  making  it  first  combine  with  some  of 
the  oxygen  that  is  in  the  air  and  afterwards  obtaining  nitrate  from  this 
combination.  They  are  thus  able  to  make  fertilizers  artificially.  The 
only  difficulty  with  this  plan  is  that  it  requires  a  very  high  electric  current. 
In  certain  places  in  the  world,  however,  where  the  price  of  land  is  not  high 
and  where  water-power  is  cheap,  it  has  been  found  possible  and  profitable 
to  set  up  powerful  dynamos  and  generate  electricity  which  is  used  to  make 
fertilizers.  As  the  price  of  fertilizers  increases  it  is  very  likely  that  many 
more  such  stations  will  be  established  than  there  are  at  the  present  time. 

The  only  place  where  free  nitrate  is  to  be  found  abundantly  is  Chile, 
which  furnished  the  world  its  supply  before  the  war.  As  a  result  of  being 
bottled  up  by  the  English  blockade,  Germany  was  forced  to  look  to  the  air 
for  her  supply  of  nitrogen,  not  only  to  fertilize  her  fields,  but  to  furnish 
ammunition  for  her  guns,  since  nitrogen  is  a  necessary  part  of  every  high 
explosive.  Nitrogen,  in  fact,  has  been  called  a  "sleeping  giant."  Can  you 
explain  why? 

Home  gardens.  You  can  do  your  share  in  producing  food  for 
the  world.  Even  although  you  have  only  a  city  back  yard,  you 
will  find  that  with  proper  attention  plants  will  grow,  and  will  there 
do  their  part.  Gather  information  from  your  State  and  Federal 
Departments,  and  talk  to  people  who  have  had  experience  in  gar- 
dening. Remember  that  you  must  give  the  plants  the  necessary 
mineral  matter  in  the  form  of  fertilizers;  that  you  must  cultivate 
often  to  keep  the  water  from  escaping  and  to  keep  the  weeds 
down ;  and  that  the  sun  must  have  a  chance  to  shine  on  the  leaves, 
where  the  food  factories  are. 

INDIVIDUAL  PROJECTS 

Boys'  and  Girls'  Clubs: 

The  State  agricultural  colleges  or  the  U.S.  Bureau  of  Plant  Industry  will 
gladly  send  you  information  as  to  the  forming  of  clubs.  Farmers  Bulletin  385 
is  on  Boys'  and  Girls'  Agricultural  Clubs.  If  you  decide  to  cooperate  with  the 
Government  by  forming  a  corn  club,  a  potato  club,  a  garden  and  canning  club, 
or  a  pig  club,  be  sure  to  follow  directions  exactly,  elect  officers  and  have  regular 
meetings.  From  time  to  time  interesting  reports  may  be  given  to  the  rest  of 
the  class. 

Working  projects:  _     . 

i .  Make  a  collection  of  blue-prints  of  leaves  of  trees  that  furnish  food.    Fruit 
trees,  nut  trees,  maple  trees,  etc.,  may  be  used.     Place  the  leaf  next  to  the 


162          FOODS  AND  HOW  WE  USE  THEM 

glass  in  a  printing  frame,  then  the  blue-print  paper,  and  expose  to  the  sun- 
light. Wash  in  water  and  dry,  print  the  name  of  the  tree  and  what  food 
it  furnishes.  The  prints  may  be  mounted  on  cards  to  be  kept  for  a  school 
collection. 

2.  Make  a  collection  of  harmful  weeds  of  your  locality,  and  report  how  to 
exterminate  them.  Each  weed  should  be  carefully  pressed  between  pads 
of  newspaper  under  a  heavy  weight  and  mounted  on  cards.  By  consulting 
successful  farmers  or  gardeners  or  writing  to  The  International  Harvester 
Company,  Chicago,  for  pamphlets,  find  out  the  best  ways  of  fighting  each 
weed. 

Reports: 

1.  Men  who  have  given  us  better  plants. 

Find  out  the  story  of  the  spineless  cactus  or  the  potato  improved  by 
Luther  Burbank.  Write  to  the  Bureau  of  Plant  Industry,  Washington, 
to  find  out  what  the  Government  does  to  improve  plants. 

2.  How  seeds  travel. 

Consult  a  botany  textbook.  Collect  as  many  kinds  of  seeds  with  travel- 
ing devices  as  you  can  find  to  show  to  the  class. 

3.  Families  of  plants. 

From  a  botany  textbook  select  ten  common  families.  Then  choose 
several  of  the  plants  in  the  family  with  which  you  are  familiar,  and  explain 
to  the  class  how  they  are  alike,  so  that  they  belong  to  the  same  family. 

4.  Insect  foes  of  a  garden,  and  how  to  combat  them. 

This  project  should  be  chosen  by  boys  or  girls  who  have  gardens  of  their 
own.  Several  pupils  may  share  in  the  work.  Each  may  select  one  or  two 
of  the  most  troublesome  insects  in  his  own  garden,  exhibit  specimens, 
explain  the  life  history,  and  tell  his  own  experience  and  that  of  other  people 
in  fighting  the  pests. 

5.  Birds  that  help  in  food  production. 

Study  books  on  the  subject,  show  pictures  of  the  birds,  and  describe 
how  they  may  be  attracted.  Several  pupils  may  work  together  on  this 
project,  as  in  no.  4. 

6.  How  the  world  gets  its  sugar. 

7.  Cereal-producing  plants. 

See  Sargent's  Corn  Plants. 

8.  Opportunities  on  a  farm. 

Read  "The  Farm  Boy  who  Went  Back,"  in  the  Wonders  of  Science. 

9.  My  garden  last  year. 

A  boy  or  girl  who  had  a  successful  garden  may  tell  how  it  was  managed, 
so  that  others  in  the  class  may  succeed  better  this  year. 
IO.  How  an  army  gets  its  food. 


BOOKS  THAT  WILL  HELP  YOU 

Garden  books: 

Farmers'  bulletins:  U.S.  Department  of  Agriculture. 
154,  The  Home  Fruit  Garden. 
2 55,  The  Home  Vegetable  Garden. 
218,  The  School  Garden. 
408,  School  Exercises  in  Plant  Production. 
A-B-C  of  Gardening.     E.  E.  Rexford.     Harper  &  Bros. 

Simple  directions  for  making  flower  gardens,  outdoors  and  in. 
Beginners'  Garden  Book.     Allen  French.     The  Macrru'llan  Co, 


PLANTS  163 

Garden  Steps.     Ernest  Cobb.     Silver  Burdett  &  Co. 

An  account,  intended  for  children,  of  vegetables  and  their  ways. 
The  Home  Vegetable  Garden.     Adolph  Kruhm.     Orange  Judd  Co. 

General  directions  for  making  a  garden,  with  definite  information  about 
each  of  the  vegetables. 
Insect  books: 

Farm  Friends  and  Farm  Foes.     C.  M.  Weed.     D.  C.  Heath  &  Co. 
U.S.  Department  of  Agriculture,  Farmers'  Bulletin  31,  Cutworms. 
Bird  books: 

Birds  of  Village  and  Field.     F.  I.  Merriam.     Houghton  Mifflin  Co. 

A  bird  book  for  beginners. 
Useful  Birds  and  Their  Protection.     Mass.  Board  of  Agriculture. 

A  convincing  account  of  the  importance  of  birds. 

Wild  Bird  Guests,  How  to  Entertain  Them.    E.  H.  Baynes.    E.  P.  Dutton 
&Co. 

Reasons  for  protecting  birds,  with  practical  illustrations  of  bird  houses, 
baths,  etc. 
Tree  books: 

Field  Book  of  American  Trees  and  Shrubs.   F.  S.  Mathews.    G.  P.  Putnam's 
Sons. 

A  concise  description,  with  illustrations  in  color  showing  general  appear- 
ance, leaf,  and  fruit. 

Trees  Every  Child  Should  Know.     J.  E.  Rogers.    Doubleday,  Page  &  Co. 
Food  plants: 

Corn  Plants  —  Their  Uses  and  Ways  of  Life.     F.  L.  Sargent.     Houghton 
Mifflin  Co. 

An  interesting  account  of  all  the  cereals. 
Cuban  Cane  Sugar.     Robert  Wiles.     Bobbs-Merrill  Co. 
Peeps  at  Industries.     E.  A.  Browne.     Adam  and  Charles  Black. 

Includes  sugar,  tea,  etc. 

The  Story  of  Sugar.     G.  T.  Surface.     D.  Appleton  &  Co. 
Scientific  agriculture: 

The  Story  of  Agriculture  in  the  United  States.    A.  H.  Sanford.    D.  C.  Heath 
&Co. 

Chapters  on  the  "New  Era  of  Scientific  Agriculture"  and  on  the  "De- 
partment of  Agriculture." 

Wonders  of  Science,  in  The  Children's  Hour  Series,  edited  by  E.  M.  Tappan. 
Houghton  Miflflin  Co. 

An  interesting  account  of  "The  Farm  Boy  who  Went  Back." 
New  Creations  in  Plant  Life.     W.  S.  Harwood.    The  Macmillan  Co. 
Leaf  photography: 

Article  in  Scientific  American  Supplement,  April  29,  1916.     Illustrated. 


PROJECT  IX 
FOODS  AND  THE  HUMAN  BODY 

The  two  great  uses  of  foods.  Foods,  like  air  and  water,  are 
used  by  living  beings.  Every  one  knows  that  foods  make  it  pos- 
sible for  living  things  to  grow.  Foods  also  give  strength,  and  by 
strength  we  mean  the  ability  to  do  things.  You  have  already 
learned  that  foods  are  like  fuel  for  an  engine.  (See  page  42.) 
Foods  serve  these  two  great  purposes :  to  build  up  the  structures  of 
living  things  —  for'  growth  and  repair  —  and  to  furnish  them 
with  energy.  In  this  project  we  shall  try  to  find  out  what  this 
general  statement  means.  It  will  involve  comparing  some  of  the 
most  common  kinds  of  foods  to  see  just  which  ones  are  best  suited 
to  serve  these  purposes.  You  will  want  to  find  out,  for  example, 
what  became  of  the  food  you  ate  for  breakfast  this  morning ;  where 
it  entered  the  blood  in  your  body  and  how  it  is  at  this  very  min- 
ute helping  to  build  and  repair  your  body  and  also  helping  your 
lungs  to  work,  your  heart  to  beat,  and  your  brain  to  be  active. 
It  takes  energy  to  do  these  things  as  well  as  to  run  and  play,  and 
the  foods  you  eat  give  you  the  materials  from  which  the  energy 
comes. 

PROBLEMS 

PROBLEM  i :  To  COMPARE  SOME  COMMON  FOODS  WITH  REFERENCE  TO  THEIR 
ABILITY  TO  BUILD  UP  THE  BODY  AND  FURNISH  ENERGY. 

Directions: 

From  the  food  charts  on  pages  174  to  178,  make  a  list  of  about  twenty 
common  kinds  of  foods.  Write  these  names  down  in  a  column  on  the  left- 
hand  side  of  a  piece  of  notebook  paper.  Arrange  to  have  two  columns  to 
the  right  of  these  names.  At  the  top  of  one  of  these  columns  write  "  Per  cent 
of  Protein"  and  at  the  top  of  the  other  column  write  "No.  of  Calories." 

(Note  —  The  per  cent  of  protein  is  an  index  to  the  ability  of  the  food 
to  furnish  building  material  for  growth  and  repair.  The  number  of 
calories  indicates  the  amount  of  energy  which  the  food  possesses.) 


FOODS  AND  THE  HUMAN  BODY  165 

Summary: 

1.  Using  the  table  which  you  have  made,  select  some  foods  that  may  be 
said  to  be  fairly  rich  in  protein.     (Select  those  that  contain  at  least  eight 
per  cent.) 

2.  Select  some  foods  that  furnish  much  energy.     What  nutrient  or 
nutrients  are  they  apt  to  contain  in  large  amounts? 

PROBLEM  2 :  To  FIND  HOW  HEAT  is  MEASURED. 
Directions: 

Pour  into  a  metal  container  or  calorimeter  a  pound  of  water.  Place  a 
thermometer  in  the  water  and  determine  its  temperature.  Place  the  calo- 
rimeter with  the  water  and  the  thermometer  on  a  tripod  and  gently  apply 
heat. 

Watch  the  thermometer  and  note  when  the  temperature  has  risen  4°  F. 
The  water  may  now  be  said  to  have  absorbed  what  is  called  a  calorie. 
(Definition  —  A  calorie  is  the  amount  of  heat  needed  to  raise  a  pound 

of  water  approximately  4°  F.) 

Continue  to  watch  the  thermometer  and  apply  heat  until  the  tempera- 
ture has  risen  8°,  12°,  16°,  20°  F.,  from  its  starting-point.  How  many 
calories  has  the  water  absorbed  at  each  of  these  times? 

Questions: 

1 .  Does  it  take  more  or  less  heat  to  raise  two  pounds  of  water  than  one 
pound  through  the  same  number  of  degrees? 

2.  Suppose,  in  the  above  experiment,  that  two  pounds  of  water  had 
been  used  instead  of  one  pound.    How  many  calories  would  have  been 
absorbed  when  the  temperature  rose  4°,  8°,  12°,  16°,  20°  F.? 

PROBLEM  3 :  To  DETERMINE  THE  RELATIVE  COST  OF  SOME  COMMON  KINDS 
OF  FOODS. 

Directions: 

By  consulting  your  mother  or  the  butcher  and  grocer  figure  out  the 
approximate  cost  per  pound  of  the  foods  you  listed  in  problem  i. 

Mention  some  foods  that  give  much  nourishment  as  compared  with  their 
cost. 

Mention  some  that  give  a  fair  amount  of  nourishment  in  comparison 
with  their  cost. 

Mention  some  which  yield  only  a  small  amount  of  nourishment  as  com- 
pared with  their  cost. 

Summary: 

1.  Does  the  cost  of  food  necessarily  indicate  the  amount  of  nourishment 
it  contains? 

2.  What  have  you  noticed  about  the  cost  of  foods  rich  in  protein? 


166          FOODS  AND  HOW  WE  USE  THEM 

Questions: 

Can  you  think  of  any  other  things  that  should  be  considered  in  selecting 
foods  aside  from  the  amount  of  nourishment  and  cost?  If  so,  what? 

PROBLEM  4:  WHAT  ARE  THE  PARTS  AND  WORK  OF  THE  HUMAN  ALIMEN- 
TARY CANAL? 
Directions: 

Copy  the  drawing  of  the  human  alimentary  canal  from  page  181. 

Label  the  following  parts:  mouth,  gullet,  stomach,  small  intestines,  large 
intestines,  and  rectum. 

Indicate  by  labels  in  the  drawing  in  what  part  of  the  alimentary  canal 
the  following  juices  are  found:  saliva,  gastric  juice,  bile,  and  pancreatic 
juice.  Can  you  also  show  in  your  drawing  whether  these  juices  are  made 
in  the  walls  of  the  alimentary  canal  or  whether  they  are  made  outside  and 
have  to  be  brought  to  the  food  tube  and  poured  in? 

What  kind  or  kinds  of  nutrients  are  digested  by  each  of  these  juices? 

PROBLEM  5:  WHAT  is  PRODUCED  WHEN  SALIVA  is  ADDED  TO  STARCH? 
Directions: 

Collect  some  saliva  in  a  test-tube.    Boil  a  little  starch  in  another  test-tube. 

Test  the  material  to  see  that  it  is  starch.    (See  problem  5  on  page  145.) 

Test  the  starch  to  see  whether  it  contains  any  grape  sugar.  (See  prob- 
lem 6  on  page  145.) 

Test  the  saliva  to  see  whether  it  contains  any  grape  sugar. 

Mix  a  little  saliva  with  some  starch  that  has  cooled  and  test  for  grape  sugar. 
Summary: 

How  do  you  explain  the  presence  of  grape  sugar  in  the  mixture  of  two 
substances  neither  of  which  contains  it? 

Questions: 

1.  Of  what  use  is  it  for  living  things  to  be  able  to  change  starch  into 
grape  sugar?     (See  page  181.) 

2.  Germinating  seeds  have  this  power.     Of  what  use  is  it  to  them? 

PROBLEM  6:  WHAT  ARE  THE  PARTS  OF  A  TOOTH? 
Directions: 

Copy  the  drawing  of  a  longitudinal  section  of  a  tooth  from  page  185. 

Label  the  following  named  parts:  enamel,  crown,  dentine,  root,  cement, 
and  pulp  cavity. 

Questions: 

1.  Of  what  use  is  each  of  the  parts  of  a  tooth? 

2.  What  has  your  study  of  the  structure  of  a  tooth  taught  you  in  regard 
to  its  care? 


FOODS  AND  THE  HUMAN  BODY  167 

PROBLEM  7:  To  FIND  HEADACHE  POWDERS  AND  OTHER  PATENT  MEDICINES 

THAT  CONTAIN  DRUGS. 

Directions: 

Secure  the  wrappers  or  containers  of  headache  powders  and  other  patent 
medicines.  Look  for  the  names  of  the  different  substances  they  contain. 
Make  a  list  of  these  "  remedies "  or  "cures,"  together  with  a  list  of  the  drugs 
found  in  them. 

Questions: 

1.  Do  you  find  any  phenacetin,  acetanilid,  morphine,  opium,  heroin, 
alcohol,  and  chloral  present? 

2.  Is  it  of  much  use  to  the  ordinary  person  to  have  these  names  printed 
upon  the  labels  or  wrappers?    If  not,  why?    What  would  you  suggest 
should  be  done? 

PROBLEM  8 :  To  DETERMINE  THE  EFFECT  OF  EXERCISE  UPON  THE  RATE  OF 
THE  HEARTBEAT. 

Directions: 

By  lightly  placing  one  or  two  fingers  upon  the  inside  of  the  wrist  find  the 
pulse.  (Do  not  use  the  thumb  to  try  to  find  the  pulse  because  there  is  a 
pulse  there  which  may  interfere  with  the  experiment.)  Count  the  num- 
ber of  pulsations  that  occur  in  a  minute  when  sitting  quietly. 

(Note  —  Every  pulsation  follows  a  heartbeat.) 

Take  some  exercise,  such  as  a  setting-up  drill  for  two  or  three  minutes. 
Immediately  after  this  find  the  pulse  and  count  the  number  of  heartbeats 
in  a  minute. 

Questions: 

1.  What  was  the  effect  of  exercise  upon  the  rate  of  the  heartbeat? 

2.  Compare  this  result  with  the  effect  of  exercise  upon  the  rate  of  breath- 
ing.   (See  page  34.) 

3.  Can  you  see  any  reason  why  the  cells  of  the  body  need  more  food  and 
oxygen,  and  need  to  get  rid  of  their  wastes  more  rapidly  during  and  after 
exercise  than  when  the  body  is  resting?  Has  this  fact  anything  to  do  with 
the  results  you  obtained  in  this  observation?   Explain. 

How  to  select  foods.  In  selecting  foods  the  following  matters 
should  be  considered:  (i)  amount  and  kind  of  nourishment  the 
foods  contain;  (2)  cost;  (3)  taste  and  digestibility;  (4)  quality 
and  cleanliness. 

The  amount  of  nourishment  in  foods.  By  the  term  nourish- 
ment is  meant  (i)  the  amount  of  building  material,  which  is  used 


168          FOODS  AND  HOW  WE  USE  THEM 

for  either  growth  or  repair,  and  (2)  the  amount  of  energy-produc- 
ing material  foods  contain. 

Protein  is  the  one  important  nutrient  that  is  used  for  growth 
and  repair  of  body  tissues.  One  of  the  reasons  for  this  is  that 
protein  is  the  only  nutrient  that  contains  certain  elements  needed 
for  growth,  such  as  nitrogen. 

All  three  of  the  organic  nutrients  may  be  oxidized  and  thus  re- 
lease energy.  This  release  of  energy  results  in  keeping  us  warm 
and  making  it  possible  for  us  to  carry  on  all  our  life  activities. 
Although  protein  is  useful  for  this  purpose,  carbohydrates  and 
especially  fats  are  even  more  so.  A  pound  of  fat  has  twice  as 
much  energy  stored  in  it  as  a  pound  of  either  protein  or  carbo- 
hydrate. 

Meaning  of  the  term  "  calorie."  The  word  calorie  has  come 
into  very  general  use  lately  in  connection  with  the  energy- 
giving  power  of  foods.  A  calorie  is  a  unit  of  heat  just  as  an  inch, 
foot,  yard,  etc.,  are  units  of  measure  or  just  as  a  pound  or  ton  is  a 
unit  of  weight.  You  know  that  the  dimensions  of  a  room  can  be 
measured,  but  perhaps  you  have  never  thought  it  possible  to 
measure  accurately  the  amount  of  heat  contained,  for  example, 
in  a  ton  of  coal  or  a  loaf  of  bread.  It  is,  however,  just  as  possible 
to  do  this  as  to  measure  the  length,  breadth,  and  height  of  a 
room. 

A  calorie,  as  the  term  is  usually  applied  to  foods,  is  the  amount 
of  heat  needed  to  raise  the  temperature  of  water  approximately 
four  degrees,  F.  Thus,  when  we  say  that  a  pound-of  butter  con- 
tains 3400  calories,  we  mean  that  when  oxidized  it  would  give  off 
enough  heat  to  raise  the  temperature  3400  pounds,  nearly  one  and 
three  quarters  tons  of  water,  approximately  four  degrees,  F.  That 
is  a  considerable  quantity  of  heat,  and  yet  men  at  hard  labor  re- 
quire in  one  day  a  greater  amount  of  heat-producing  food  than 
this  represents.  The  average  man  requires  somewhat  less,  some 
authorities  putting  the  estimate  as  low  as  2800  calories. 

A  mixed  diet  is  usually  desirable.  To  say  that  a  person  needs 
food  giving  3400  calories  per  day  is  not  the  same  as  saying  that 
such  a  person  should  eat  a  pound  of  butter  every  day.  It  cer- 
tainly is  undesirable  for  most  people  to  eat  only  one  kind  of  food. 


FOODS  AND  THE  HUMAN  BODY  169 

Our  bodies  cannot  use  all  kinds  of  foods  that  may  be  eaten. 
Most  people  find  that  they  obtain  the  best  results  when  they  eat 
a  mixed  diet  or  a  combination  of  different  foods  containing  all  the 
different  nutrients.  While  no  hard-and-fast  rules  can  be  made 
that  are  of  universal  application  regarding  the  amount  and  kind 
of  food  that  should  be  eaten,  yet  there  is  one  rule  of  general  ap- 
plication —  eat  moderately. 

People  need  varying  amounts  and  kinds  of  food.  The  amount 
and  kind  of  food  that  any  person  needs  depends  upon  several  con- 
ditions, chief  among  which  are  the  following:  age  and  size,  occu- 
pation, and  climate.  A  child  needs  a  larger  proportion  of  build- 
ing material  because  in  addition  to  the  need  of  furnishing  food  for 
repair  of  tissues  provision  must  be  made  for  growth  as  well.  An 
active  child  also  generally  needs  a  larger  proportionate  amount  of 
fuel  or  energy-giving  foods.  Again,  size  usually  is  very  important 
in  determining  the  amount  of  food  needed.  The  larger  and 
stronger  of  two  boys  of  the  same  age  usually  needs  much  more 
food  than  the  lighter,  smaller  boy,  just  as  a  large  engine  requires 
more  fuel  than  a  small  one. 

Similarly,  occupation  helps  to  determine  the  amount  and  kind 
of  food  needed.  Lumbermen,  who  work  at  hard  manual  labor 
from  sunrise  to  sunset,  naturally  require  more  food  especially  of 
an  energy-producing  kind  than  a  clerk  in  an  office.  Soldiers  in 
active  campaigning  have  to  be  well  supplied  with  food  to  enable 
them  to  endure  the  hardships  of  service. 

Finally,  climate  is  an  important  factor.  The  Eskimo  consumes 
more  food  and  of  an  entirely  different  kind  from  that  used  by 
people  living  in  torrid  regions.  The  Eskimo  must  be  plentifully 
supplied  with  fats,  while  those  living  in  warmer  climates  have  a 
larger  proportion  of  carbohydrates  in  their  diet.  Likewise,  the 
amount  and  kind  of  food  required  by  any  one  person  change  with 
the  seasons.  We  naturally  require  more  fatty  food  and  a  larger 
amount  of  food  in  the  winter  than  in  the  summer. 

From  the  facts  already  given  it  must  be  evident  that  it  is  diffi- 
cult to  make  hard-and-fast  rules  regarding  the  amount  and  kind 
of  food  advisable.  It  is  largely  a  matter  that  must  be  deter- 
mined by  the  person  concerned.  Yet  it  is  possible  to  make  cer- 


170 


FOODS  AND  HOW  WE  USE  THEM 


tain  general  statements.  Most  boys  and  girls  entering  high 
school  require  food  which  will  yield  between  2200  and  2500  calo- 
ries a  day.  A  project  that  any  boy  or  girl  might  attempt  to  work 
out  would  be  to  make  lists  of  the  different  amounts  and  kinds  of 
foods  eaten  by  him  or  her  every  day  for  a  week.  Then  figure  out 
the  total  number  of  calories  eaten  a  day  and  also  the  amount  of 
protein.  Many  people  eat  too  much  protein  —  more  than  their 
bodies  can  properly  take  care  of.  According  to  Frank  A.  Rex- 
ford  in  his  book,  A  One-Portion  Food  Table,  between  two  and  two 
and  a  half  ounces  of  protein  a  day  are  enough  for  a  boy  or  girl. 
In  order  to  obtain  a  better  idea  of  the  fuel  value  of  different  foods 
consult  the  tables  and  charts  which  follow. 

Food  Table  showing  loo-calorie  portions.  For  the  sake  of  con- 
venience in  computing  the  number  of  calories  eaten  in  any  one's 
diet,  many  ordinary  foods  have  been  roughly  measured  into  100- 
calorie  portions. 


Kind  of  food 

1.  Meats 

Beef 

Lamb  chop 
Roast  lamb 
Pork 
Salmon 

2.  Vegetables 

Beans,  baked 

Beans,  string 

Beets 

Carrots 

Corn 

Onions,  cooked 

Peas 

Potatoes 

Spinach 

Tomatoes  (fresh) 

Turnips 

3.  Fruits 

Dates 
Figs 


Amount 

large  serving 
small 

ordinary  serving 
small  serving 
small  serving 


small  side  dish 
5  servings 

3  servings 
2  servings 

1  side  dish 

2  large  servings 
i  serving 

1  good-sized 

2  servings 

4  servings 

2  large  servings 


3  large 
I  large 


FOODS  AND  THE  HUMAN  BODY 


171 


Kind  of  Food 

Prunes 

Apples 

Bananas 

Cantaloupe 

Oranges 

Pears 

Strawberries 

4.  Dairy  products 

Butter 

Buttermilk 

Cheese,  American 

Cheese,  Cottage 

Cream 

Milk 

Egg 

Olive  oil 

5.  Desserts 

Cake,  sponge 
Custard,  milk 
Pie,  apple 
Rice  pudding 
Tapioca 

6.  Sweets  and  pickles 
»     Honey 

Olives 
Sugar 

7.  Nuts  and  cereals 

Pecans 

Peanuts 

Walnuts 

Bread 

Corn  flakes 

Hominy 

Macaroni 

Oatmeal 

Rice 

Shredded  wheat 


Amount 
3  large 
2  large 
i  large 
one  half 
i  large 

1  large 

2  servings 


ordinary  pat 
1 1  glasses 
if  cu.  in. 
4  cu.  in. 
i-  glass 
small  glass 
one 
i  tablespoonful 

small  piece 
ordinary  cup 
one-third  piece 
small  serving 
ordinary  serving 

4  teaspoonfuls 

7 

3  teaspoonfuls  or  i|  lumps 


8 

12  double 

6 

thick  slice 

dish 

large  serving 

ordinary  serving 

1 1  servings 

dish 

one 


Food  charts.    The  following  charts  have  been  published  by  the 
United  States  Government : 


fe 

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IN  THE  DAILY  ROLL-CALL 
RY  COLUMN  SHOULD  ANSW 

FOOD  SHOWS  THAT  IT  WILL  ALSO  DO  THE  WORK 
HAVING  THE  SAME  NUMBER.  STUDY  TH: 

FOOD  PRIMARILY 

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FOODS  SUITABLE  FOR  INFAJ 

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in  infant  feeding  used  to 
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ci 

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GROWTH  AND 

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in  Mineral  Matter 
dch  builds  bone  and 
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2  I 


FOODS  AND  THE  HUMAN  BODY  179 

The  cost  of  food.  One  of  the  factors  that  most  people  have  to 
consider  in  selecting  their  foods  is  cost.  In  recent  years  the  cost 
of  foods  has  greatly  increased.  The  cost  of  food  does  not  neces- 
sarily determine  its  nutritive  value.  For  a  given  cost,  some  foods 
yield  many  times  the  amount  of  nourishment  that  others  give. 
Although  this  is  true,  it  is  also  true  that  protein  foods,  which  are 
very  essential  for  reasons  already  given,  are  often  more  expensive 
than  other  kinds  of  foods.  Therefore,  it  is  true  that  if  we  are  to 
meet  the  needs  of  the  body,  we  must  purchase  some  foods  that 
are  generally  considered  expensive.  Can  you  mention  some  foods 
of  this  kind?  Lastly,  there  is  another  class  of  foods  that  are 
expensive  and  yet  contain  very  little  nourishment.  Can  you 
mention  some  of  them? 

Taste  and  digestibility.  People's  tastes  differ.  When  your 
mother  goes  out  to  select  foods  she  always  takes  this  fact  into 
consideration.  Although  it  is  decidedly  proper  to  do  this,  yet 
sometimes  too  much  attention  may  be  given  to  taste  and  not 
enough  to  the  actual  amount  of  nourishment.  Taste,  however, 
is  important  because  it  is  closely  related  to  digestibility.  For 
example,  some  people  are  unable  to  digest  certain  kinds  of  food 
that  most  of  us  like  and  can  use.  Thus,  some  people  cannot  eat 
strawberries ;  others  cannot  eat  eggs ;  and  still  others  cannot  drink 
milk.  There  is  hardly  any  particular  kind  of  food  which  all 
people  can  eat  without  having  some  undesirable  effects.  How- 
ever, it  is  quite  true  that  some  foods  are  generally  more  easily 
digested  than  others.  Bread  and  cereals  are  usually  easily  di- 
gested, whereas  pastries  and  fried  foods  are  hard  to  digest.  Each 
person  should  find  out  for  himself  what  foods  agree  and  what  dis- 
agree with  him,  and  be  guided  by  this  knowledge  in  selecting  his 
foods. 

Quality  and  cleanliness.  Foods  differ  in  quality.  The  cost  of 
food  does  not  always  indicate  quality.  By  quality  we  mean 
whether  food  is  pure  or  diluted,  fresh  or  stale,  clean  or  dirty. 
Storekeepers  should  keep  food  covered.  If  exposed,  dust  may 
get  on  it  and  flies  may  contaminate  it.  All  of  these  facts  should 
be  taken  into  consideration  when  deciding  where  and  what  to 
purchase. 


i8o          FOODS  AND  HOW  WE  USE  THEM 

Tea,  coffee,  and  other  food  adjuncts.  In  recent  years  more  than  one 
billion  pounds  of  coffee  and  approximately  one  hundred  million  pounds  of 
tea  have  been  consumed  annually  in  the  United  States.  Many  people  have 
become  so  accustomed  to  having  these  beverages  that  it  would  mean  a 
great  hardship  to  have  to  give  them  up.  The  pleasing  effects  which  they 
produce  are  due  principally  to  the  drug  caffeine  which  exerts  a  stimulating 
or  quickening  effect  upon  the  heart  and  nervous  system.  Such  a  drug  is 
called  a  stimulant.  Tea  and  coffee  contain  no  nourishment  aside  from  the 
sugar  and  milk  that  are  usually  added.  The  effect  of  their  use  for  a  short 
time  is  generally  not  very  detrimental.  Like  other  drugs,  however,  their 
continued  use  will  gradually  result  in  injury  to  the  body  tissues. 

Spices,  pepper,  catsup,  and  other  condiments  contain  very  little  nour- 
ishment. They  are  used  principally  to  stimulate  the  appetite  and  should 
be  indulged  in  sparingly. 

Why  we  cook  foods.  Foods  are  cooked  (i)  to  make  them  taste 
better;  (2)  to  make  them  more  easily  digestible;  (3)  to  kill  any 
bacteria  or  other  harmful  organisms  they  may  contain.  Cooking 
affects  foods  in  different  ways :  some  are  made  tender  and  others 
are  hardened.  The  fibers  of  meat,  for  example,  are  softened,  while 
an  egg  is  hardened.  (See  page  91.)  Frying  is  usually  consid- 
ered the  poorest  way  of  cooking  foods  since  it  is  apt  to  make  them 
difficult  to  digest.  Unless  the  fat  is  very  hot  it  is  apt  to  soak  into 
the  food,  making  it  "  soggy  "  and  covering  each  little  particle  with 
a  coating  of  fat  which  prevents  the  digestive  juices  from  quickly 
acting  upon  it. 

The  value  of  some  uncooked  foods.  In  recent  years  scientists  have 
discovered  that  some  uncooked  foods  have  present  in  them  very  small 
amounts  of  certain  substances  which  are  extremely  important  for  health. 
These  substances  have  been  called  vitamins.  Vitamins  are  found  in  fruit, 
milk,  tomatoes,  lettuce,  and  certain  other  vegetables.  Cooking  destroys 
these  vitamins  except  in  the  case  of  very  acid  fruits. 

The  food  tube.  After  food  is  swallowed,  it  passes  along  a  pipe, 
called  the  cesophagus,  or  gullet  which  carries  it  into  the  stomach.  This 
organ  is  really  an  enlarged  part  of  the  oesophagus.  The  food  usu- 
ally stays  in  the  stomach  for  two  or  three  hours  before  it  is  passed 
on.  The  walls  of  the  stomach  contain  muscles  which  gently 
churn  the  food.  They  also  manufacture  a  juice  which  helps  to 
make  the  food  liquid.  When  it  is  in  a  proper  condition,  the  food 
is  made  to  pass  out  of  the  stomach,  which  raises  itself  a  little  at 


FOODS  AND  THE  HUMAN  BODY 


181 


this  time  and  by  means  of  its  muscles  forces  the  food  out.  Upon 
leaving  the  stomach  it  continues  to  go  along  a  passageway,  called 
the  intestines,  which  gently 
force  the  food  along  by 
means  of  muscles  similar  to 
those  in  the  walls  of  the 
stomach.  The  intestines  in 
a  human  being  are  about 
twenty  feet  long.  While  the 
food  is  in  the  stomach  and 
intestines,  part  of  it  is  ab- 
sorbed and  enters  the  blood 
vessels  which  are  located  in 
its  walls.  In  this  way,  by 
means  of  the  blood  stream, 
nourishing  material  is  car- 
ried all  over  the  body,  and 
the  hungry  cells,  most  of 
which  are  far  away  from 
the  intestines,  are  fed. 

Digestion  and  its  use. 
Before  food  can  enter  the 
blood,  it  must  be  made  into 
a  liquid.  This  process  is 
known  as  digestion  and  it 
occurs  as  the  food  passes 
through  different  parts  of 
the  food  tube.  It  is  accom- 
plished by  means  of  juices  or  secretions  which  act  upon  it.  The 
digestive  juices  act  in  two  ways:  (i)  they  dissolve  the  food 
which  is  soluble;  and  (2)  they  act  chemically  upon  insoluble 
foods  to  make  them  soluble.  Milk  is  a  liquid  and  yet  it  cannot 
pass  into  the  blood  as  milk.  If  it  could  we  should  expect  to  find 
milk  in  the  blood  after  swallowing  a  glass  of  this  nutritious  food. 
We  know  that  a  baby's  principal  food  is  milk,  but  we  also  know 
that  a  baby's  blood  is  not  milk.  Certain  very  remarkable  changes 
must  take  place  in  the  milk  before  it  can  enter  the  blood  and  be 


FIG.  92.  Parts  of  the  food  tube.  (From 
Hutchinson's  Handbook  of  Health.) 


1 82          FOODS  AND  HOW  WE  USE  THEM 

used  to  help  build  the  cells  of  the  baby's  body.     Some  of  these 
changes  are  effected  by  digestion. 

Digestion  in  the  mouth.  If  you  have  performed  the  experiment 
with  saliva  at  the  beginning  of  this  project,  you  will  have  learned 
that  there  is  something  in  this  secretion  that  is  able  to  change 
starch  to  grape  sugar.  The  usefulness  of  this  change  is  to  be 
found  in  the  fact  that  grape  sugar  is  able  to  pass  through  the 
stomach  and  intestinal  walls  and  enter  the  blood,  something  which 
starch  is  unable  to  do.  The  changing  of  starch  into  grape  sugar 
is  brought  about  by  a  substance  in  the  saliva,  called  ptyalin. 
Ptyalin  is  one  of  a  large  group  of  substances,  called  enzymes, 
which  bring  about  chemical  changes  in  living  beings. 

Stomach  and  intestinal  digestion.  Not  only  must  starch  be 
changed  chemically,  but  fats  and  proteins  and  the  other  carbo- 
hydrates besides  starch  must  be  changed  before  they  can  enter 
the  blood.  These  changes  are  brought  about  by  enzymes  which 
are  found  in  the  stomach  and  intestines.  The  secretion  in  the 
stomach,  called  gastric  juice,  has  an  enzyme,  pepsin,  which  can 
digest  protein.  The  most  important  secretion  in  the  intestines, 
pancreatic  juice,  contains  several  enzymes  which  make  it  possible 
for  this  fluid  to  change  all  the  different  nutrients  so  that  they  can 
enter  the  blood. 

The  circulation  of  the  blood.  The  blood  is  forced  through  tubes 
to  all  parts  of  the  body  by  the  beating  of  the  heart.  Not  only  is 
the  blood  forced  to  all  parts,  but  it  is  collected  and  brought  back 
to  the  heart,  ready  to  circulate  again.  The  blood  moves  in  tubes 
which  are  connected  with  the  heart.  There  are  valves  in  the 
heart  which  keep  the  blood  flowing  always  in  one  direction.  Thus, 
the  blood  which  enters  the  upper  right  side  of  the  heart  has  come 
from  all  parts  of  the  body  except  the  lungs.  It  flows  into  the 
lower  right  side  through  the  valves  and  from  there  it  is  sent  to  the 
lungs,  where,  as  we  have  already  learned,  it  receives  a  fresh  sup- 
ply of  oxygen  and  gives  up  most  of  'its  carbon  dioxide.  The  blood 
coming  back  from  the  lungs  enters  the  upper  left  side  of  the  heart, 
flows  through  valves  into  the  lower  left  side,  and  is  forced  out  to 
all  parts  of  the  body  except  the  lungs.  Then  it  returns  to  the 
upper  right  side  of  the  heart.  This  is  the  place  which  it  left,  per- 


FIG.  93.  The  way  the  blood  circulates  in  the  body.  (From 
Hutchinson's  Handbook  of  Health.} 


FOODS  AND  THE  HUMAN  BODY 


183 


FIG.  94.  Exchanges  of  materials  between  the 
blood  and  the  body  dells. 


haps  less  than  a  minute  previously.     Thus  the  blood  circulates 

and    carries     nourishment 

and  oxygen  to  all  the  cells 

and  takes  away  from  them 

their   carbon   dioxide   and 

other  wastes. 
Kinds  of  blood  vessels. 

The  tubes  which  carry  the    'tfjfy&^'&fi 

blood  away  from  the  heart    ;^\y:->Vii^>£ 

are    called    arteries;   those 

carrying  the  blood  back  to 

the  heart  are  called  veins  ; 

while  the  tiny  tubes  which 

connect  the   arteries  with 

the  veins  are  called  capil- 
laries.   It  is  while  the  blood 

is  passing  through  the  capillaries  that  the  body  cells  take  from 

it  what  they  need  and  give  up  to  it 
their  wastes.  Such  exchanges  can  take 
place  only  in  the  capillaries  because 
the  walls  of  the  other  blood  vessels  are 
too  thick  to  permit  osmosis  to  occur. 

Treatment  of  cuts.  It  is  advisable  to 
learn  a  few  principles  in  first-aid  in  case  of 
injury  to  blood  vessels.  In  scratches  and 
in  cuts  which  are  merely  upon  the  surface 
bacteria  may  find  lodgment.  In  such  cases, 
however,  it  is  usually  unnecessary  to  do 
more  than  carefully  clean  the  wound  with 
pure  water  and  put  a  sterilized  bandage 
around  it  until  it  stops  bleeding.  Such 
wounds  will  usually  heal  quickly,  especially 
if  the  person  is  in  good  physical  condition 
and  the  loss  of  blood  is  insignificant. 

Wounds  which  are  deeper,  where  the  blood 
comes  out  in  spurts,  require  more  careful 
FIG.  95.  A  tourniquet.  The  stone    handling.     In  such  cases  it  may  be  neces- 
is  placed  over  the  artery,  between     sary  to  place  a  tourniquet,  as  shown  in  the 
the  cut  and  the  heart  and  pressed     diagrani>  to  Stop   the   flow  of  blood.     The 
firmly  by  means  of  the  knotted 

handkerchief.  (From  Hutchinson's    tourniquet  is  usually  placed  between  the 
Child's  Day.)  cut  and  the  heart.    Why?     In  accidents  of 


1 84          FOODS  AND  HOW  WE  USE  THEM 

this  kind  a  doctor  should  be  summoned  as  soon  as  possible,  but  before  the 
physician  arrives  the  patient  should  be  kept  quiet  and  every  effort  made  to 
stop  the  loss  of  blood.  This  can  sometimes  be  done  without  the  use  of  the 
tourniquet  by  fastening  a  bandage  over  the  wound  and  allowing  the  blood 
to  clot.  By  the  clotting  of  the  blood  is  meant  the  tendency  which  the  blood 
shows,  when  exposed  to  the  air,  of  forming  a  fibrous,  jelly-like  mass.  If 
this  can  be  formed  over  the  wound,  the  bleeding  will  cease.  Care  should 
be  taken  not  to  disturb  the  clot,  if  one  can  be  formed. 

Stomach-aches.  A  stomach-ache  is  often  caused  by  food  remaining 
wholly  or  partly  undigested  in  the  stomach  and  while  there  being  acted 
upon  by  bacteria.  Indigestion  is  commonly  caused  by  (i)  eating  too 
rapidly;  (2)  eating  too  much ;  (3)  eating  when  tired;  (4)  exercising  imme- 
diately after  eating;  (5)  becoming  excited  during  or  immediately  after  a 
hearty  meal.  As  a  result  of  indigestion  poisonous  gases  and  liquids  are 
frequently  formed,  some  of  which  upon  entering  the  blood  cause  sickness. 
The  stomach-ache  is  often  relieved  by  taking  something  to  get  rid  of  the 
gas.  One  of  the  most  common  remedies  is  baking  soda,  the  usual  amount 
being  a  teaspoonful  in  half  a  glass  of  water.  This  neutralizes  or  destroys 
the  acid  which  is  apt  to  be  made  in  the  stomach  at  such  times.  Often  pains 
in  the  intestines  are  called  stomachaches.  If  there  are  severe  pains  in  this 
region,  it  is  best  to  send  for  a  doctor. 

Headaches.  Headaches  are  sometimes  caused  by  indigestion,  but  more 
frequently  by  a  blocking  of  the  lower  part  of  the  intestines  with  the  wastes 
left  from  the  foods.  In  such  an  event,  bacteria  again  make  poisons  which 
pass  into  the  blood  and  are  carried  all  over  the  body.  For  a  remedy  it  is  a 
common  thing  to  take  headache  powders  or  tablets,  although  such  sub- 
stances do  not  usually  remove  the  cause  of  the  trouble.  Most  of  these 
remedies  contain  powerful  drugs  which  are  capable  of  seriously  injuring 
the  heart.  They  often  cause  a  feeling  of  relief  because  the  heart  is  made 
to  beat  more  slowly  and  consequently  there  is  a  lower  blood  pressure  in 
the  head.  The  effect  of  the  powder  is  apt  to  wear  off  rather  soon,  and  the 
person  is  often  ho  better  off  than  if  he  had  not  taken  the  dose.  It  is 
usually  less  harmful  to  undergo  a  little  suffering  than  to  run  the  risk  of 
injuring  such  an  important  organ  as  the  heart.  The  wisest  thing,  of  course, 
is  so  to  act  as  not  to  bring  on  headaches. 

Any  one  who  suffers  from  headaches  should  find  out  the  cause  of  the 
trouble,  and  if  possible  remove  it.  If  the  cause  is  a  blocking  of  the  intes- 
tines, it  can  usually  be  avoided  by  careful  eating,  sufficient  exercise,  and 
drinking  plenty  of  water.  If  the  cause  cannot  be  found,  it  is  advisable  to 
consult  a  doctor.  Sometimes  headaches  are  caused  by  eye-strain  or  other 
trouble  of  which  one  may  not  be  aware. 

Teeth  and  their  care.  Almost  every  one  is  troubled  at  some 
time  or  other  with  a  toothache.  Every  toothache  is  a  danger 


FOODS  AND  THE  HUMAN  BODY 

signal  that  something  is  wrong  and  needs  attention.  The  chew- 
ing of  foods  is  a  very  important  step  in  preparing  them  to  become 
part  of  the  blood.  The  teeth  break  the  food  into  smaller  particles 
with  the  result  that  there  is  a  larger  surface  upon  which  the  diges- 
tive secretions  can  act.  Therefore,  every  tooth  is  of  great  value 
and  should  receive  the  best  of  care.  The  manner  in  which  teeth 
decay  can  be  understood  only  when  we  know  about  their  struc- 
ture. 

Structure  of  the  teeth.  If  you  will  study  the  picture  at  the 
side  of  the  page,  you  will  see  that  on  the  outside  of  a  tooth  there 
is  a  layer  of  material  called  enamel.  This  is 
the  hardest  substance  in  the  body.  Under 
the  enamel  there  is  a  softer  substance,  called 
dentine,  which  is  a  kind  of  bony  material. 
Toward  the  center  of  the  tooth  there  is  a 
cavity  which  contains  blood  vessels  and  nerves. 
From  this  cavity  very  small  tubes  or  chan- 
nels, which  contain  blood  vessels  and  nerves, 
run  into  each  root.  These  tubes  are  called 
root  canals.  Each  tooth  fits  into  a  little  cav- 
ity in  the  jaw-bone  and  is  held  in  place  by 
means  of  a  kind  of  cement. 

Cavities  in  teeth.  Decay  in  teeth  is  usually 
caused  by  bacteria.  A  little  particle  of  food 
gets  into  a  crevice  in  the  tooth  and  bac- 
teria get  into  the  food  and  work  upon  it. 
As  a  result  of  this  an  acid  is  formed  which 
eats  its  way  through  the  enamel.  When  this 
happens  the  dentine  is  exposed  and  the  bacteria  can  then  cause 
more  rapid  decay.  Toothache  may  not  be  felt  in  the  early  stages 
of  this  process.  It  usually  follows  after  a  considerable  damage 
has  been  done  to  the  dentine.  For  this  reason  it  is  well  to  have  the 
dentist  examine  the  teeth  at  least  twice  a  year  to  see  whether  any 
small  cavities  are  forming.  If  this  precaution  be  taken,  several 
desirable  results  should  follow:  (i)  Toothache  may  usually  be 
avoided.  (2)  The  dentist  will  not  have  to  cause  as  much  pain. 
It  is  much  easier  and  less  painful  to  fill  a  small  cavity  than  a  large 


FIG.  96.  The  structure 
of  a  tooth:  e,  enamel;  d, 
dentine;  p,  pulp  cavity; 
c,  cement;  n,  nerve;  j, 
jaw-bone. 


1 86          FOODS  AND  HOW  WE  USE  THEM 

one,  when  sometimes  the  nerve  has  to  be  killed.  (3)  The  dentist's 
bill  will  not  be  so  large.  (4)  Even  more  important  is  the  fact 
that  keeping  the  teeth  in  fine  condition  will  contribute  to  better 
health,  since  decaying  teeth  harbor  bacteria,  some  of  which  may 
cause  colds,  sore-throats,  stomach  and  intestinal  troubles. 

How  to  care  for  the  teeth.  Besides  going  to  the  dentist  regu- 
larly you  should  brush  the  teeth  vigorously  with  a  fairly  stiff 
brush  at  least  twice  a  day,  just  before  going  to  bed  and  the  first 
thing  upon  arising  in  the  morning.  The  motion  that  is  especially 
helpful  is  an  up  and  down  movement,  for  in  this  manner  the  little 
particles  that  lodge  between  the  teeth  can  usually  be  removed. 
Another  even  better  way  of  getting  rid  of  these  particles  is  by 
using  dental  floss.  The  teeth  should  not  be  used  to  bite  very 
hard  things,  and  if  dental  paste  is  used  it  should  be  free  from 
gritty  material  which  might  scratch  the  enamel. 

The  effect  of  alcohol  and  tobacco  upon  digestion  and  circulation. 

Alcohol  and  tobacco  are  narcotics.  A  narcotic  is  the  opposite  of  a  stimu- 
lant. It  tends  to  deaden  or  paralyze  body  tissues.  Alcohol  used  to  be 
considered  a  stimulant,  but  its  effects  are  now  known  to  be  those  of  a 
narcotic. 

One  of  the  most  marked  effects  of  alcohol  is  its  power  of  taking  water 
out  of  substances  with  which  it  comes  in  contact.  The  white  of  an  egg,  for 
example,  may  be  hardened  by  placing  it  in  alcohol.  When  alcohol  is  taken 
into  the  food  tube  and  then  absorbed  into  the  blood  vessels,  it  tends  to 
harden  the  walls  of  these  tubes.  This  hardening  is  harmful,  especially  to 
the  arteries.  The  arteries  are  made  so  that  they  can  stretch.  When  hard- 
ened they  lose  their  elasticity,  and  the  proper  circulation  of  the  blood  is 
interfered  with. 

Aside  from  its  effect  upon  the  walls  of  the  blood  vessels,  alcohol  exerts  a 
harmful  effect  upon  the  red  and  white  corpuscles.  (See  page  44.)  The 
red  corpuscles  are  unable  to  carry  as  much  oxygen  as  they  should  and  the 
white  corpuscles  cannot  attack  bacteria  so  vigorously. 

The  question  is  often  asked:  Is  alcohol  a  food?  This  question  is  an- 
swered differently  by  different  authorities.  A  small  amount  of  alcohol 
may  be  oxidized  and  thus  furnish  energy.  In  this  sense  it  may  be  called  a 
food,  but  alcohol  is  a  poison,  and  many,  probably  the  majority  of,  authori- 
ties claim  that  for  this  reason  it  cannot  properly  be  classed  as  a  food.  After 
alcoholic  beverages  are  drunk,  the  blood  vessels  carrying  blood  to  the  skin 
are  enlarged.  A  flushed  condition  results  and  a  feeling  of  warmth  is  pro- 
duced because  the  nerves  which  carry  a  sensation  of  warmth  to  the  brain 
are  located  in  the  skin.  As  a  matter  of  fact,  alcohol  instead  of  warming  the 


FOODS  AND  THE  HUMAN  BODY  187 

body  results  in  lowering  the  body  temperature.  The  blood  is  cooled  when 
it  comes  near  the  surface.  That  is  the  reason  that  men  who  have  to  sleep 
out  in  the  open  in  cold  weather  ought  especially  to  avoid  the  use  of  alco- 
holic beverages.  There  are  instances  on  record  of  men,  not  understanding 
this  effect  of  alcohol,  having  been  frozen  to  death,  because  they  had  a 
drink  to  keep  them  warm,  while  others  in  the  same  party  who  abstained 
did  not  suffer  greatly  from  the  cold.  Arctic  explorers  do  not  allow  any 
alcoholic  beverages  to  be  taken  along  on  their  expeditions. 

Tobacco,  although  not  as  injurious  as  alcohol,  also  weakens  the  bodily 
resistance  to  disease.  Experiments  upon  animals  have  indicated  that  it 
hardens  the  arteries.  There  is  reason  for  believing  that  it  also  exerts  a 
similar  effect  upon  the  human  body.  It  is  apt  to  affect  the  heart  injuri- 
ously, and  produce  what  is  called  a  "tobacco  heart";  that  is,  in  certain 
diseases,  such  as  typhoid  fever  and  pneumonia,  a  strong  heart  insures 
greater  likelihood  of  recovery. 

INDIVIDUAL  PROJECTS 

Working  projects: 

1.  Make  out  a  menu  for  yourself  for  one  day  which  shall  contain  the  proper 
number  of  calories. 

Civic  Biology.     G.  W.  Hunter.     American  Book  Co. 

Food  and  Household  Management.     Kinne  and  Cooley.     The  Macm.il- 

lan  Co. 
Feeding  the  Family.    Mary  S.  Rose.     The  Macmillan  Co. 

2.  Win  Camp-Fire  honors  in  Home  Craft. 

Reports; 

1.  Vitamins  and  their  value. 

How  to  Live.     Fisher  and  Fisk.     Funk  &  Wagnalls. 

2.  The  varying  food  needs  of  workers  in  different  occupations. 

Civic  Biology.     G.  W.  Hunter.     American  Book  Co. 

Food  for  the  Worker.     Stern  and  Spitz.     Whitcomb  &  Barrows. 

BOOKS  THAT  WILL  HELP  YOU 

All  About  Milk.     Metropolitan  Life  Insurance  Co. 

The  Body  at  Work.     Frances  Gulick  Jewett.     Ginn  &  Co. 

First  Aid  for  Boys.     Cole  and  Ernst.     D.  Appleton  &  Co. 

First  Aid  in  the  Home.     Metropolitan  Life  Insurance  Co. 

Foods  and  Health.     Kinne  and  Cooley.     The  Macmillan  Co. 

Food,  What  It  Is  and  Does.     Edith  Grier.     Ginn  &  Co. 

Handbook  of  Health.     Woods  Hutchinspn.     Houghton  Mifflin  Co. 

The  Primer  of  Sanitation.     John  W.  Ritchie.     World  Book  Co. 

School  Feeding.     S.  Bryant.     J.  B.  Lippincott  Co. 

(The  Effects  of  Alcohol)  Town  and  City.    Frances  Gulick  Jewett.    Ginn  &  Co. 


PROJECT  X 

FOODS  IN  THE  HOME 

Clean  foods.  If  you  go  to  a  store  to  buy  food,  you  prefer  to 
patronize  a  store  where  everything  is  neat  and  clean,  where  no 
flies  are  lurking,  and  where  no  dust  can  settle  on  the  food.  Within 
the  past  few  years  great  improvement  has  been  brought  about 
in  the  conditions  under  which  food  is  kept  in  public  places.  In 


FIG.  97.  A  clean  store. 
(Courtesy,  Women's  Municipal  League,  Boston.) 

many  communities  there  are  laws  governing  the  care  of  foods. 
Inspectors  visit  wharves,  freight  stations,  and  markets.  From 
the  time  the  food  leaves  the  farm  until  the  time  it  leaves  the  store 
for  your  home  it  is  open  to  inspection  by  officials  who  see  that  the 
laws  in  regard  to  its  care  are  obeyed. 

If  in  your  community  the  food  is  not  kept  clean,  you,  the  boys 
and  girls  who  are  now  studying  about  foods,  can  take  steps  to 
remedy  the  wrong  conditions.  If  you  know  of  a  butcher  shop  where 
the  meat  is  exposed  to  dirt  and  dust,  or  where  it  may  be  coughed 
or  sneezed  upon  by  customers  or  the  salesmen  in  the  shop,  you 


FOODS  IN  THE  HOME  189 

may  be  able  to  waken  public  opinion  in  your  community  to  the 
dangers  of  such  unsanitary  conditions:  If  you  know  of  a  grocery 
store  where  crackers,  beans,  or  macaroni  are  left  in  open  barrels, 
possibly,  to  be  visited  by  the  store  cat  or  mice,  and  sure  to  be 
touched  by  flies  and  dust,  you  can  describe  the  harmful  effects 
of  such  exposure  to  your  mothers  and  urge  them  to  trade  at 
stores  where  the  food  is  kept  in  a  clean  way.  If  all  the  mothers  in 
a  community  should  refuse  to  buy  in  a  dirty  store,  it  would  not  be 
long  before  the  storekeeper  would  clean  up,  in  self-defense. 

As  soon  as  the  food  enters  your  home,  however,  inspectors 
stop  examining  it.  Then  it  becomes  the  duty  of  the  home-keeper 
to  see  that  the  food  is  clean  and  healthful.  In  this  project  you 
will  find  out  why  foods  spoil,  and  how  to  prevent  them  from 
doing  so. 

PROBLEM  i :  WHAT  ARE  THE  CAUSES  OF  THE  SPOILING  OF  FOODS? 

Directions: 

Moisten  a  piece  of  bread,  place  it  in  a  saucer,  and  expose  it  to  the  air  for 
three  or  four  hours.  Then  cover  with  a  glass  and  set  it  aside  in  a  warm  place. 

Pour  out  a  little  milk  into  a  saucer  and  set  aside  in  a  warm  place. 

Boil  a  potato  in  its  jacket  until  about  half  done.  Cut  in  two,  place  each 
half  on  a  saucer,  expose  to  the  air  for  several  hours,  then  cover  with  glasses 
and  set  aside  in  a  warm  place. 

Pour  a  little  molasses  into  a  jar,  dilute  with  warm  water  and  set  aside, 
uncovered,  in  a  warm  place. 

After  a  day  or  two  examine  the  foods  for  changes  in  appearance  and  odor. 

Any  colored  spots  show  that  bacteria  have  attacked  the  food. 

A  fuzzy  white  growth  or  green  spots  show  that  mold  has  attacked  the  food. 

Bubbles  or  a  smell  of  alcohol  show  that  yeast  has  attacked  the  food. 

Summary: 

Name  the  organisms  which  have  attacked  the  food,  and  describe  the 
changes  caused  by  each  organism. 

Questions: 

1.  Where  may  these  organisms  have  come  from? 

2.  Why  is  caution  necessary  in  the  use  of  raw  foods? 

PROBLEM  2:  How  DO  BACTERIA  GET  UPON  FOOD? 

Directions: 

Boil  potatoes  in  their  jackets  until  half  done,  cut  each  with  a  knife  that 
has  been  sterilized  by  boiling,  place  the  halves  on  saucers,  and  expose  in 
some  of  the  following  ways.  Then  cover  with  glasses  and  set  aside  in  a 
warm  place: 


190         FOODS  AND  HOW  WE  USE  THEM 

1 .  Leave  exposed  to  the  air  of  the  room. 

2.  Expose  in  corridors  when  pupils  are  passing. 

3.  Expose  in  the  street. 

4.  Let  a  fly  crawl  over  the  cut  surface. 

5.  Sneeze  on  it. 

6.  Cough  on  it. 

7.  Rub  your  finger  over  it. 

8.  Wash  your  hands  with  warm  soapy  water,  and  rub  your  finger  over  it. 
Show  by  a  label  how  each  potato  was  treated.    Examine  the  potatoes 

every  day  for  about  a  week,  and  count  the  number  of  spots  upon  the  cut 
surfaces.  Each  spot  is  a  colony  of  many  bacteria,  or  perhaps  mold. 

Watch  the  development  of  the  colonies  for  several  days. 

Keep  a  record  in  a  table. 

When  you  have  finished  the  experiment,  burn  the  potatoes  at  once,  and 
wash  all  the  dishes  in  very  hot,  soapy  water.  Then  boil  the  dishes  to 
sterilize  them  thoroughly.  W7ash  your  hands  thoroughly. 

Questions: 

1.  Should  eggs  be  washed  before  using?    Why? 

2.  What  is  the  danger  in  a  damp  old  mop  or  a  soiled  dish  towel? 

PROBLEM  3:  WHY  DOES  BREAD  MOLD? 

Directions: 

Place  a  piece  of  moistened  stale  bread  in  each  of  three  preserve  jars,  and 
a  piece  of  dry  stale  bread  in  a  fourth  jar.  Expose  all  four  to  the  air  of  the 
room  for  an  hour  or  so.  Cover  all  the  jars,  using  rubbers  and  half  sealing 
them. 

Set  the  jar  with  the  dry  bread  in  a  warm  place. 

Place  one  jar  containing  moist  bread  in  warm  water;  boil  ten  minutes. 
Set  aside  in  a  warm  place. 

Set  the  third  jar  in  a  warm  place,  without  sterilizing. 

Set  the  fourth  jar  in  the  refrigerator. 

Notice  each  day  any  changes  that  appear,  and  keep  a  record. 

Summary: 

1.  How  does  mold  get  on  bread? 

2.  What  temperature  is  most  favorable  to  the  growth  of  mold? 

3.  Does  mold  require  water  for  growth? 

Questions: 

1.  In  what  three  ways  may  food  be  protected  from  mold? 

2.  Why  should  the  bread-box  be  scalded  often? 

PROBLEM  4:  WHAT  DOES  FLOUR  CONTAIN? 
Directions: 

Tie  a  cup  of  flour  in  a  ten-inch  square  of  cheesecloth,  and  wash  it  in  a  pan 
of  water. 


FOODS  IN  THE  HOME  191 

What  changes  take  place  in  the  water?  Wash  all  material  possible  out 
of  the  bag. 

After  a  few  minutes  drain  off  the  water  from  the  powder  in  the  pan. 

Test  the  powder  with  iodine.     Explain  your  results. 
'  Remove  the  material  from  the  bag  and  knead  into  a  ball.     Does  it  cling 
together?     This  material  is  gluten. 

Heat  the  ball  on  a  pan  in  the  oven  and  note  results. 
Conclusion: 

Name  two  substances  in  the  flour. 

Question: 

Why  can  you  knead  and  stretch  a  dough  of  wheat  flour  while  cornmeal 
dough  falls  apart? 

PROBLEM  5 :  WHAT  TEMPERATURE  is  MOST  FAVORABLE  FOR  THE  GROWTH 

OF  YEAST? 
Directions: 

Stir  a  yeast  cake  in  three-fourths  cupful  of  lukewarm  water.  Divide  the 
solution  into  three  parts.  Mix  one-fourth  cup  water  and  one-fourth  cup 
flour.  Add  one  tablespoonful  of  molasses.  Divide  the  mixture  into  three 
parts.  In  one  bowl  mix  a  part  of  the  yeast  solution  with  a  part  of  the  flour 
mixture.  Set  it  in  cracked  ice  and  salt. 

In  a  second  bowl  mix  a  part  of  the  flour  mixture  with  a  part  of  the  yeast 
solution  and  set  it  in  lukewarm  water. 

Heat  the  remaining  part  of  the  yeast  solution  until  it  boils.  Mix  it 
with  the  flour  mixture  in  a  third  bowl  and  set  it  in  lukewarm  water. 

Note  the  results. 

Conclusion: 
What  is  the  best  temperature  for  the  growth  of  yeast? 

Questions: 

1.  If  you  wish  to  retard  the  growth  of  yeast,  how  will  you  treat  it? 

2.  If  you  wish  to  entirely  stop  the  growth  of  yeast,  how  will  you  treat  it? 

3.  Should  you  pour  boiling  water  on  a  yeast  cake  to  dissolve  it? 

4.  If  your  bread  is  light,  and  the  oven  not  ready,  what  may  you  do  with 
the  dough? 

PROBLEM  6:  WHY  DOES  YEAST  CAUSE  BREAD  TO  RISE? 

Directions: 

Mix  a  yeast  cake  with  one-third  cupful  of  lukewarm  water.  Add  it  to  a 
mixture  of  one-fourth  cup  warm  water,  one-fourth  cup  flour,  and  one  table- 
spoonful  of  molasses. 

Place  the  whole  mixture  in  a  flask  or  wide  mouthed  bottle,  with  a  stop- 
per and  bent  glass  tube  ending  in  a  tube  of  lime  water. 

Explain  what  happens. 


192          FOODS  AND  HOW  WE  USE  THEM 

Conclusions: 

1.  What  gas  is  formed  in  the  dough  by  the  action  of  yeast? 

2.  Why  does  the  dough  increase  in  size? 

PROBLEM  7 :  A  TRIP  TO  A  LARGE  BAKERY  TO  FIND  OUT  HOW  BREAD  is  MADE. 

Directions: 

By  observation  and  by  questioning  find  answers  to  as  many  of  the  fol- 
lowing questions  as  possible. 

1.  What  kinds  of  flour  are  used? 

2.  Where  does  the  flour  come  from? 

3.  What  liquid  is  used  in  the  bread? 

4.  What  is  used  to  make  the  bread  rise? 

5.  How  is  the  bread  kept  clean? 

6.  In  what  processes  does  machinery  take  the  place  of  hands? 

7.  How  is  the  bread  baked? 

Summary: 

Write  a  letter  to  your  mother  about  your  trip,  contrasting  what  you  have 
learned  about  making  bread  in  a  bakery  with  her  method  of  making  it. 

PROBLEM  8 :  To  CAN  A  VEGETABLE. 

(Note  —  This  method,  the  cold-pack  method,  may  be  used  for  all 
vegetables  with  slight  changes.  (See  page  200.)  Tomatoes  are  among 
the  easiest  vegetables  to  can.) 

Directions: 

1.  Select  fresh,  ripe,  firm  tomatoes. 

2.  Wash  them  in  cool  water. 

3.  Scald.     Have  ready  a  kettle  of  boiling  water.     Place  the  tomatoes  in 
a  square  of  cheesecloth,  and  lower  into  the  boiling  water  to  loosen  the  skins. 
One  half  to  one  minute  should  be  long  enough. 

4.  Cold  dip.     Lift  out  the  cheesecloth  containing  the  tomatoes,  and 
plunge  into  a  large  dish  of  cold  water. 

5.  Remove  skins.     Hold  each  tomato  in  your  left  hand  and  cut  out  the 
core  if  you  wish.  In  small  tomatoes  you  may  leave  the  core.  Slip  off  the  skin. 

6.  Pack  in  clean,  hot  jars.     Press  the  tomatoes  well  down,  but  do  not 
crush  them.     You  may  leave  them  without  adding  water,  or  add  a  juice 
made  of  the  poorer  tomatoes  and  those  which  break  in  handling. 

7.  Add  salt.    Add  one  level  teaspoon  of  salt  to  each  quart,  or  one  rounded 
teaspoon  of  mixed  sugar  and  salt,  two  parts  sugar  and  one  part  salt. 

8.  Place  rubber  and  cover.     Be  sure  there  are  no  chips  in  the  jar.     Use 
good  rubbers  which  fit  closely.     Put  the  cover  in  place. 

9.  Part  seal.     Do  not  seal  any  glass  jars  tight  at  this  stage.     How  does 
air  behave  when  heated?     How  does  water  change  when  boiled?    What 
would  happen  if  air  or  steam  could  not  escape  from  the  jars?  • 


FOODS  IN  THE  HOME 


193 


If  you  are  using  jars  with  a  wire  snap,  put  the  wire  over  the  cover,  and 
leave  the  clamp  up. 

If  you  are  using  screw-top  jars,  screw  the  cover  down  with  the  thumb 
and  little  finger,  so  as  not  to  seal  too  tight. 

If  you  are  using  vacuum  seal  jars,  put  the  cover  on  and  the  spring  in 
place.  The  spring  will  give  enough  to  allow  the  steam  to  escape. 

10.  Sterilize.  Use  a  wash  boiler  or  large  kettle.  Place  a  false  bottom  in 
kettle.  Why  should  the  jars  not  touch  the  bottom? 

Put  in  four  inches  of  warm  water  and  set  over  low  fire. 

Set  cans  in  cooker  as  soon  as  each  is  ready.  Leave  cooker  uncovered 
until  all  cans  are  in. 

Add  warm  water  to  cover  the  tallest  jar  at  least  one  inch. 

Cover  the  cooker  and  bring  water  to  boiling  point. 

After  water  begins  to  boil,  sterilize  tomatoes  twenty-two  minutes. 

n.  Remove  from  cooker.  Move  the  cooker  back,  uncover  (Caution  — 
steam !),  and  remove  jars.  A  convenient  way  of  lifting  jars  with  wire  fast- 
eners is  to  use  a  long  buttonhook. 

12.  Tighten  the  covers,  and  invert  the  jars  a  few  minutes  to  see  if  they 
leak.     (Do  not  invert  vacuum  jars.) 

13.  When  cool,  label,  and  store  in  a  cool,  dry  place. 


PROBLEM  9:  To  CAN  BERRIES  OF  ANY  KIND. 

Directions: 

Use  the  directions  given  for  tomatoes,  with  the  following  exceptions: 

Berries  require  no  scalding.  After  seeding  or 
stemming,  place  the  berries  in  a  strainer  and 
rinse  by  pouring  cold  water  over  them.  Pack 
into  warm  jars  without  crushing,  using  a  large 
wooden  spoon.  Pour  hot  syrup  over  the  fruit 
to  fill  the  jar,  place  rubber  and  cap  in  position, 
and  part  seal. 

To  make  the  syrup,  use  twice  as  much  water 
as  sugar,  and  bring  to  the  boiling  point. 

Sterilize  the  jars  sixteen  minutes,  counting 
from  when  the  water  begins  to  boil  after  all  the 
jars  are  in  the  cooker. 


FIG.  98.  A  home-made  drier. 
The  racks  can  be  made  with- 
out the  cabinet. 


PROBLEM  10:  To  DRY  SWEET  CORN. 

(Note — This  method  of  drying  may  be  used 
for  many  vegetables  and  fruits.) 

Directions: 

Boil  the  corn  on  the  cob  for  three  minutes.     Slice  it  off  upon  cheesecloth 
laid  over  drying  racks.     (See  illustration.)     Spread  the  com  thinly  over 


194 


FOODS  AND  HOW  WE  USE  THEM 


the  cloth.  Set  the  racks  over  the  back  of  the  stove  where  there  is  a  good 
circulation  of  air. 

After  several  hours  examine  the  corn  to  seeif  it  is  of  a  leathery  consistency. 
If  so,  remove,  and  place  in  pasteboard  boxes,  in  each  of  which  is  a  cracker. 

If  the  crackers  become  moist  after  a  few  hours  the  corn  is  not  sufficiently 
dried.  If  the  crackers  remain  dry,  the  corn  is  ready  to  store. 

Store  in  clean  dry  containers. 

PROBLEM  11:  To  PASTEURIZE  MILK. 

(Note  —  Many  disease-producing  bacteria  in  milk  may  be  destroyed 
in  the  following  way.) 

Directions: 

Arrange  an  apparatus  consisting  of  a  pail  with  a  perforated  false  bottom. 

Why  is  it  necessary  to  raise  the 
bottles  from  the  bottom  of  the  pail  ? 

Wash  the  outside  of  the  bottles 
of  milk  by  holding  under  the  faucet, 
and  set  them  in  the  pail. 

Punch  a  hole  through  the  cap 
of  one  of  the  bottles  and  insert  a 
thermometer. 

Fill  the  pail  with  water  nearly 
to  the  level  of  the  milk. 

Heat  until  the  thermometer  in 
the  milk  shows  not:  less  than  1 50°  F. 
nor  more  than  155°  F. 

Remove  the  bottles  and  let  them 
stand  twenty  minutes,  covered 
with  a  cloth.  What  is  the  tempera- 


"  •  r 


FIG.  99.  Dirty  milk,  which  was  photo- 
graphed through  a  microscope.  Bacteria  are 
shown,  some  of  which  may  be  able  to  produce 
disease. 


(Courtesy,  Boston  Health  Department.) 


the  punctured  cap  with  a  new  one. 


ture  at  the  end  of  this  time? 

Place  the  bottles  in  cold  water. 
Remove  the  thermometer.  Replace 
Store  the  bottles  in  a  cold  place. 


Question: 

Since  one  quart  of  milk  equals  eight  eggs  in  food  value,  which  is  the  more 
economical  food  at  present  prices? 


PROBLEM  12:  To  COMPARE  RAW  MILK,  PASTEURIZED  MILK,  AND  BOILED 
MILK. 

Directions: 

In  test-tubes  place  portions  of  raw  milk  as  you  get  it  from  the  milkman, 
pasteurized  milk,  and  milk  brought  to  the  boiling  point  and  cooled. 


FOODS  IN  THE  HOME 


195 


Compare  the  appearance  of  the  three  kinds. 

Taste  the  three  kinds.  Which  has  the  pleasantest  taste?  the  least 
pleasant  taste? 

Place  portions  in  a  warm  place.  Test  frequently  by  smelling  and  with 
litmus  paper  for  souring.  Which  sours  first?  Which  sours  last?  Do 
any  of  the  samples  change  in  other  ways  than  by  souring? 

Summary: 

Name  the  advantages  of  each  kind  of  milk. 

PROBLEM  13:  To  CLEAN  A  REFRIGERATOR. 

Directions: 

Remove  all  the  dishes  of  food  from  the  refrigerator.  If  any  ice  remains 
in  the  ice  chamber,  lift  it  out  into  a  large  pan. 


FIG.  100.  Diagram  showing  the  circulation  of  air  in  two  usual  types  of 
refrigerators.  Air  entering  the  ice  chamber  is  freed  from  odors,  cooled,  and 
sinks  through  the  bottom  openings,  drawing  in  the  warmer  air  at  the  top. 
Butter,  milk,  and  meats  should  occupy  the  coolest  space,  while  food  having 
a  strong  odor  should  be  placed  where  the  air  is  just  about  to  enter  the  ice 
chamber. 

(Courtesy,  Massachusetts  Department  of  Weights  and  Measures.) 

Remove  all  the  adjustable  shelves  and  trays.  Wash  them  with  hot 
soapy  water,  rinse  with  clear  water,  and  place  in  the  sun  to  dry.  Do  you 
know  how  sunlight  acts  on  some  bacteria? 

With  a  clean  cloth  wet  with  hot  soapy  water  wipe  the  lining  of  the  re- 
frigerator. Then  wipe  with  a  cloth  wet  with  clear  water,  and  finally  with 
a  dry  cloth.  Leave  the  refrigerator  open  until  perfectly  dry.  Why  does 
it  dry  more  quickly  when  open? 


196         FOODS  AND  HOW  WE  USE  THEM 

Pour  a  solution  of  washing  soda  down  the  waste  pipe.  How  does  wash- 
ing soda  act  on  grease? 

Replace  the  trays  and  the  ice. 

Before  returning  the  food,  examine  it  to  see  that  it  is  in  good  condition. 
See  that  every  dish  is  clean. 

PROBLEM  14:  A  TRIP  TO  THE  HEALTH  DEPARTMENT  OF  MY  CITY. 

Directions: 

From  observation  and  questions  find  out  as  much  as  you  can  about  the 
work  of  the  Health  Department. 

What  measures  are  taken  to  make  sure  that  the  food  for  the  city  is  clean? 

How  is  the  milk-supply  regulated? 

How  is  the  water-supply  regulated? 

How  is  the  ice-supply  regulated? 

Summary: 

Sum  up  the  work  of  the  Health  Department  along  the  lines  mentioned. 
If  you  have  a  friend  living  in  another  city,  send  your  report  to  him  and 
ask  for  a  report  of  the  work  of  his  city. 

Why  foods  spoil.  Have  you  realized  how  many  other  living 
organisms  live  in  your  house  besides  your  family?  Many  of  them 
are  invisible  until  we  place  them  under  a  powerful  microscope. 
From  all  the  microscopic  forms  in  the  dust  we  may  pick  out  three 
which  cause  food  to  spoil;  they  are  bacteria,  yeasts,  and  molds. 

Comparison  of  bacteria,  molds,  and  yeasts.  These  three  forms 
of  living  things  are  similar  in  the  following  particulars:  (i)  they 
are  all  plants;  (2)  they  are  all  very  prevalent  —  that  is,  they  are 
found  all  about  us ;  (3)  they  are  all  very  small ;  (4)  they  all  spread 
by  making  very  tiny  seed-like  bodies  called  spores  —  these  spores 
are  found  in  dust  and  are  blown  about  by  the  wind ;  (5)  they  may 
spoil  foods.  Bacteria  and  yeasts  are  alike  in  that  there  are  help- 
ful as  well  as  harmful  kinds.  (See  page  88.) 

Bacteria  are  the  smallest  of  these  three  organisms.  Next  to 
bacteria  come  yeasts.  Molds  are  the  largest.  They  differ  in 
the  kinds  of  foods  that  they  attack.  Yeasts  like  to  live  in  sweet 
foods.  Molds  and  bacteria  are  not  so  particular;  molds  can  grow 
on  all  kinds  of  things,. even  on  shoe  leather  and  wood;  and  bac- 
teria attack  practically  everything. 

The  action  of  bacteria  on  food.     Bacteria  are  so  tiny  that  they 


FOODS  IN  THE  HOME 


197 


cannot  take  the  food  inside  their  bodies  as  we  do.  Instead  they 
attach  themselves  to  food  and  act  on  it  by  absorbing  what  they 
need  and  making  the  rest  unfit  for  use.  Sometimes  they  produce 
in  food  which  is  apparently  good  poisonous  substances.  Such 
poisons  are  called  ptomaines.  Fish,  meat,  shellfish,  ice-cream,  and 
canned  vegetables  may  contain  ptomaines,  especially  in  the  sum- 
mer. Any  one  who  eats  food  so  poisoned  may  become  danger- 
ously ill. 

The  action  of  molds  on  food.  Molds  are  much  the  largest  of 
the  housewife's  three  enemies.  They  are  large  enough  to  be 
seen  with  the  naked  eye  and  may  even  spread  so  that  one  plant 
covers  a  large  space ;  for  ex- 
ample, the  surface  of  a  slice 
of  bread. 

In  your  study  of  plants  as 
food -makers  for  the  world, 
you  found  that  large  plants 
have  several  organs.  The 
purpose  of  the  organs  of 
growth,  the  roots,  stem,  and 


FIG.  101.  Three  common  mold  plants:  A,  the 
cheese  mold  —  penicillium;  B,  the  corn  smut  — 
aspergillus;  C,  the  bread  mold  showing  the 
root-like  organs  r  ;  runners,  stalks  and  fruiting 
bodies  which  bear  the  spores. 


Xt1;1:  •'  .-•'   '  '•' 

leaves,  is  to  get  enough  food 
to  support  the  plant.  The 
flower  is  the  organ  in  which 
new  plants  are  started.  Each 
organ  has  its  own  work  to  do. 

Molds,  although  such  small  plants,  show  a  similar  division  of  labor. 
They  are  usually  not  green,  so  they  cannot  make  their  own  food ; 
they  must  therefore  steal  it.  The  organ  of  growth  in  a  mold 
plant  consists  of  a  cobweb-like  network  which  forces  tiny  threads 
between  the  particles  of  bread,  jelly,  fruit,  etc.,  and  thus  absorbs 
food.  The  organ  of  reproduction  is  a  little  ball  which  grows  up 
from  the  network  and  finally  opens  and  scatters  dust-like  spores 
to  the  wind.  Each  spore  can  start  a  new  mold  plant. 

How  to  avoid  molds.  In  order  to  grow,  a  mold  plant  must  have 
air,  moisture,  warmth,  and  food.  They  grow  best  in  still  air.  A 
circulation  of  air  in  a  ventilated  bread-box  therefore  prevents 
bread  from  molding. 


I98 


FOODS  AND  HOW  WE  USE  THEM 


Since  they  will  not  grow  without  moisture,  one  way  of  keeping 
food  is  to  dry  it.  Fruit  wrapped  in  paper  is  usually  safe  from 
mold  because  the  paper  absorbs  any  moisture.  On  the  other 
hand,  apples  in  a  barrel  may  all  spoil  if  one  becomes  moldy,  be- 
cause the  spores  scatter  over  them  all.  Every  break  in  the  skin 
is  an  invitation  to  enter.  Soon  whole  colonies  of  unwelcome 
guests  are  established  in  the  apples. 

Covering  foods  helps  to  keep  them  from  molding.  Jellies  are 
usually  covered  with  paraffin  or  paper.  If  a  mold  spore  falls  on 
these  dry  surfaces,  it  can  do  no  harm.  If  any  spores  happen  to  fall 
on  the  jelly  before  it  is  covered  they  can  grow  and  spoil  the  top  of 
the  jelly.  Brushing  the  top  with  brandy  before  covering  the 
glass  kills  any  spores  that  may  be  there. 

Molds  grow  best  at  a  temperature  from  70°  F.  to  100°  F.  This 
explains  why  foods  mold  so  much  more  in  summer  than  in  win- 
ter. Keeping  foods  in  the  refrigerator  helps  to  keep  them  from 
molding. 

The  action  of  yeast  on  food.  Yeast  is  one  of  the  invisible  in- 
habitants of  your  house  which  may  be  a  friend  or  may  be  a  foe 

Of  course  a  yeast  cake  is  not  invisible, 
But  did  you  know  that  there  are  mil- 
lions of  separate  little  yeast  plants  in 
one  yeast  cake?  You  need  to  use  a 
microscope  to  see  the  plants.  Each 
plant  is  a  colorless  oval,  about  1/3000 
of  an  inch  in  diameter.  When  it  is  full- 
grown,  a  little  bud  starts  to  grow  from 
one  side.  We  may  call  it  the  daughter 
cell.  If  you  look  at  yeast  with  a  micro- 
scope you  may  see  a  mother  with  sev- 
eral daughters,  and  perhaps  even  a  wee 
granddaughter. 

For  the  yeast  plants  to  grow,  they 
must  have  food.  This  they  get  from  sugar,  if  possible.  One 
rather  mysterious  fact  about  yeast  plants  is  that  as  they  grow 
they  produce  a  substance  called  an  enzyme.  (See  page  182.) 
Sugar  changes  very  rapidly  into  two  other  substances,  alcohol 


FIG.  102.  Yeast.  The  tiny 
plants  are  shown  as  they  appear 
through  a  microscope.  New  plants 
can  be  seen  budding  from  the 
mother  plants. 


FOODS  IN  THE  HOME  199 

and  the  gas  carbon  dioxide,  when  the  yeast  enzyme  is  present 
to  help. 

Yeast  as  a  foe.  When  preserves  "  work,"  it  is  because  yeast 
plants  are  there,  budding  and  causing  the  sugar  to  change  to 
alcohol  and  carbon  dioxide.  How  did  the  yeast  get  in? 

Yeast  is  present  as  "  wild  yeast  "  in  the  dust  in  the  air.  Like 
the  mold  spores,  the  yeast  plants  may  fall  on  preserves  before 
they  are  covered,  and  cause  much  trouble.  One  reason  why  the 
"  cold-pack  "  method  of  canning  is  so  successful  is  that  no  yeast 
may  grow  in  the  jars,  since  yeast  plants  are  killed  by  boiling. 

Wild  yeast  may  fall  upon  bread  dough  and  cause  it  to  sour. 
Whenever  food  ferments,  forming  bubbles  and  becoming  "  sour," 
yeast  plants  have  caused  the  change. 

Yeast  as  a  friend  —  bread-making.  Bread  is  called  the  staff 
of  life.  It  is  the  commonest  of  all  foods.  All  bread,  to  be  palat- 
able, must  be  full  of  holes.  For  the  lightness  of  raised  bread,  we 
usually  depend  upon  the  action  of  yeast. 

While  many  kinds  of  grains  make  good  bread,  wheat  flour 
makes  the  best.  Two  of  the  most  important  parts  of  the  wheat 
flour  are  the  starch  grains  and  the  gluten.  Starch,  as  a  carbo- 
hydrate, is  one  of  the  nutrients  valuable  as  an  energy-giver.  (See 
page  1 68.)  Gluten  is  a  wonderfully  elastic  substance  which  holds 
the  dough  together,  but  stretches  as  the  bread  rises.  As  usual 
when  yeast  is  growing,  the  sugar,  one  of  the  nutrients  in  flour, 
changes  to  alcohol  and  carbon  dioxide.  Both  of  these  substances 
pass  off  in  the  baking.  Alcohol  has  no  value  in  the  bread,  but  the 
carbon  dioxide,  as  it  escapes  through  the  dough,  makes  the  pores 
or  holes  which  cause  the  bread  to  be  light. 

Yeast  must  have  warmth,  moisture,  and  food,  if  it  is  to  grow. 
In  bread  it  gets  its  moisture  from  the  liquid  in  the  bread,  its  food 
from  the  sugar.  We  must  give  it  the  right  amount  of  warmth. 
Boiling  kills  the  cells;  cooling  stops  their  growth.  The  best 
temperature  for  rapid  growth  is  about  70°  F.  or  80°  F.,  the 
temperature  of  lukewarm  water. 

How  to  protect  foods  against  molds  and  harmful  bacteria  and 
yeasts,  (i)  It  is  necessary  to  keep  these  organisms  out  of  foods. 
For  this  reason  bread  is  wrapped  in  waxed  paper;  jars  of  jam 


200          FOODS  AND  HOW  WE  USE  THEM 

and  other  preserves  are  tightly  sealed ;  other  foods  are  canned  or 
covered  in  various  ways. 

(2)  It  is  necessary  to  kill  them  in  foods  which  may  already  con- 
tain them.     The  most  common  way  of  doing  this  is  by  boiling. 
Another  way  is  the  action  of  direct  sunlight,  which  fortunately 
kills  many  kinds  of  bacteria.     A  sunny  kitchen  is  a  more  health- 
ful place  than  a  dark  kitchen.    Any  dark  corner  may  be  a  lurking- 
place  for  harmful   organisms.      Do  you  understand  why  many 
housewives  put  jelly  in  the  sun  before  covering  it? 

(3)  It  may  be  necessary  to  treat  the  foods  in  such  a  way  as  to 
prevent  the  growth  of  any  of  these  microscopic  plants.     Perhaps 
the  most  common  way  in  which  this  is  done  is  by  refrigeration. 
It  has  been  found  that  bacteria  cannot  grow  well  in  a  cold  place. 
For  that  reason  food  which  spoils  quickly,  like  milk,  should  be 
kept  in  the  ice-box  when   not   in  use.     The   temperature   of   a 
refrigerator  does  not  kill  the  organisms,  but  it  keeps  them  from 
increasing. 

(4)  Another  common  way  of  preserving  foods  from  the  attack 
of  yeasts,  mold,  and  bacteria  is  to  use  salt  and  certain  chemicals, 
called  preservatives. 

The  cold-pack  method  of  canning.  One  of  the  best  ways  to  keep  food 
from  spoiling  is  to  can  it.  Housewives  have  for  years  canned  or  preserved 
certain  foods.  In  recent  years  a  method  of  canning  called  the  cold-pack 
method  has  come  into  use  and  proved  very  successful.  Cold-pack  canning 
simply  means  packing  the  food  uncooked,  closing  the  can,  and  sterilizing 
the  food  in  the  can.  The  whole  secret  of  success  is  cleanliness.  One  should 
start  with  clean  hands,  clean  utensils,  clean,  sound,  fresh  products,  and 
pure,  clean  water.  Full  directions  for  canning  by  this  method  may  be 
obtained  from  the  United  States  Department  of  Agriculture,  Farmers' 
Bulletin  839.  Boys  and  girls  the  country  over  are  working  in  Canning 
Clubs  to  help  conserve  the  food  of  the  country,  and  are  earning  money  by 
doing  so. 

The  essential  part  of  the  process  is  sterilizing  the  food,  that  is,  killing 
every  harmful  organism  in  it.  Boiling  is  a  sure  way  of  killing,  if  the  boiling 
is  carried  on  long  enough.  Merely  bringing  a  food  to  the  boiling  point  will 
not  kill  all  bacteria.  For  every  kind  of  food  there  is  a  particular  length  of 
time  that  it  must  be  boiled.  For  example,  apples  will  keep  if  sterilized 
twelve  minutes,  while  peas  need  to  be  sterilized  three  hours.  Use  the  time- 
table furnished  with  the  Government  directions,  and  you  will  have  good 
success. 


FOODS  IN  THE  HOME  201 

Drying  foods.  Drying  has  been  used  as  a  way  of  preserving  foods  for 
thousands  of  years.  It  is  nature's  way.  Seeds  that  are  left  to  ripen  on 
plants  become  dry,  and  then  may  be  kept  for  years.  If  planted  later,  they 
grow,  because  the  plant  in  them  has  not  died,  but  is  merely  dormant,  or 
asleep. 

We  are  accustomed  to  many  kinds  of  dried  foods.  Prunes,  raisins,  figs, 
dates,  and  apples  can  be  bought  at  any  grocery  store.  Beans,  peas,  tea, 
and  coffee  are  sold  in  the  dried  form.  Nearly  all  kinds  of  food  may  be 
dried  and  thus  kept  safe  from  attacks  of  bacteria,  molds,  and  yeasts.  We 
have  found  that  all  these  household  enemies  need  moisture.  Unless  enough 
moisture  is  given  them  they  cannot  grow.  It  is  not  necessary  to  drive 
every  particle  of  moisture  out  of  food  in  order  to  keep  it;  indeed,  perfectly 
dry  food  is  worthless.  Enough  must  be  driven  out  to  prevent  the  growth 
of  organisms,  but  enough  must  be  left  to  prevent  the  cells  from  crumbling, 
so  that  later,  when  we  prepare  the  food  for  eating,  the  cells  can  soak  back 
as  much  water  as  they  lost. 

Three  common  ways  of  drying  are  in  use :  sun  drying,  drying  by  artificial 
heat,  and  drying  by  air  blast.  In  general,  most  fruits  or  vegetables,  to  be 
dried  quickly,  must  be  cut  up  or  shredded,  so  that  every  part  may  dry 
evenly.  They  evaporate  water  into  the  air  about  them.  If  the  air  is 
closed  in,  it  will  soon  become  filled  with  moisture,  so  the  rate  of  evapora- 
tion slows  down.  A  good  circulation  of  air  is  therefore  necessary.  Con- 
vection currents  over  a  stove  (see  page  in),  or  the  blast  of  air  from  an 
electric  fan  keep  the  air  in  motion,  and  hasten  the  evaporation.  When 
dried  it  should  be  impossible  to  press  water  out  of  the  freshly  cut  ends  of 
the  pieces,  yet  they  should  not  snap  or  crackle. 

To  prepare  dried  food  for  eating,  soak  it  long  enough  to  absorb  as  much 
water  as  it  lost.  It  is  better  to  cook  it  in  the  same  water,  and  thus  save 
any  nutrients  which  dissolve  in  the  water. 

Pure  milk.  If  the  milk  producer  and  the  milk  dealer  have 
done  their  duty,  you  should  receive  at  your  door  a  bottle  of  clean, 
cold,  pure  milk.  Unless  you  treat  it  properly  then,  it  may  be- 
come unfit  for  food,  especially  for  babies.  Some  ways  by  which 
housekeepers  allow  milk  to  spoil  are  (i)  by  placing  it  in  unclean 
dishes;  (2)  by  exposing  it  unnecessarily  to  the  air;  (3)  by  failing 
to  keep  it  cool ;  and  (4)  by  exposing  it  to  flies. 

The  enemies  of  milk  are  bacteria.  Milk  is  always  the  home  of 
certain  kinds  of  bacteria.  One  kind  causes  milk  to  sour.  An- 
other kind  helps  to  flavor  butter;  this  is  a  friendly  kind.  Still 
another  kind  causes  milk  to  decay  or  putrefy  after  a  time.  Worst 
of  all,  disease  bacteria  may  have  entered  the  milk.  Diseases 


2O2 


FOODS  AND  HOW  WE  USE  THEM 


known  to  be  spread  by  milk  are  tuberculosis,  typhoid  fever, 
scarlet  fever,  diphtheria,  and  the  intestinal  troubles  which  are  so 
dangerous  to  babies. 

A  dish  may  look  clean  and  yet  have  bacteria  upon  it.  It  is  best 
to  keep  milk  in  the  bottle  in  which  you  receive  it.  If  that  is  im- 
possible, put  it  in  a  dish  which  has  been  washed  in  very  hot,  soapy 
water,  rinsed  and  thoroughly  dried  and  cooled.  Keep  a  cover 
over  the  dish.  If  the  dish  is  exposed  to  the  air,  it  is  sure  to  receive 
bacteria  from  dust  and  may  be  visited  by  flies.  Bacteriologists 
have  often  found  over  a  million  bacteria  on  a  single  fly.  They 
are  particularly  apt  to  carry  typhoid  fever  and  intestinal  diseases. 
(See  page  79.) 

It  is  necessary  to  wash  the  outside  of  the  bottle  in  which  milk 
comes  before  opening  it  and  using  the  milk.  A  milkman  may 

carry  the  bottles  by  grasp- 
ing the  tops  with  his  hand. 
Those  hands  may  have 
harnessed  his  horse;  they 
have  held  the  reins;  have 
opened  and  shut  doors  in 
all  kinds  of  homes,  and 
done  many  other  things 
since  they  were  washed. 
Put  the  milk  bottle  under 
the  hot-water  faucet  for 
a  moment  and  wipe  it  dry 
with  a  clean  cloth. 

Pasteurized  milk.  A 
good  way  of  making  sure 
that  milk  is  safe  for  babies 
to  drink,  and  for  grown- 
ups, too,  is  to  pasteurize  it.  Pasteurization  is  named  from  one  of 
the  greatest  scientists  the  world  has  known,  Louis  Pasteur.  The 
process  consists  of  heating  the  milk,  in  the  bottles  in  which  it  is 
to  be  used,  to  a  temperature  of  between  150°  F.  and  155°  F. 
Most  disease  bacteria  are  destroyed  in  this  way  without  injuring 
the  flavor  or  the  nutritive  value  of  the  milk. 


FIG.  103.  Louis  Pasteur. 


FOODS  IN  THE  HOME 


203 


Cuts  of  meat.  Meat  has  become  such  an  expensive  food  that  many 
people  can  afford  it  but  seldom.  It  is  not  necessary  for  life.  In  India  and 
Japan,  where  the  population  is  great,  millions  of  people  have  never  eaten 
meat.  Milk,  eggs,  beans,  nuts,  cheese,  and  fish  all  contain  enough  protein 
to  supply  our  bodies  with  the  proper  kinds  of  food,  and  are  usually  cheaper 
than  meat. 

We  know  that  meat  is  either  tough  or  tender.  The  difference  is  caused 
by  the  amount  of  exercise  the  different  muscles  of  the  animal's  body  have 
had.  Lean  meat  is  muscle.  You  can  easily  see 
that  muscles  lying  along  the  animal's  spine  and 
along  the  under  parts  of  the  body  are  not  used 
as  much  as  those  of  the  neck  and  legs.  The 
tough  cuts  come  from  the  neck  and  legs;  the 
tender  cuts  from  the  back  and  under  parts.  Just 
as  much  nourishment  can  be  obtained  from  cheap 
cuts  as  from  the  most  expensive  cuts,  and  they 
can  be  made  tender  by  proper  cooking.  The 
uses  of  the  cuts  of  beef  shown  in  the  illustration 
are  as  follows: 

1.  Chuck  —  Suitable  for  pot  roasts,  stews,  cas- 
serole dishes  and  spiced  beef. 

2.  Plate  —  Suitable  for  soup  and  pot  roast. 
Generally  used  for  making  corned  beef. 

3.  Shank  —  Used  mostly  for  soups  and  stews ; 
also  for  hamburger  steak. 

4.  Flank  —  Practically  a  boneless  cut.     Can 
be  used  with  very  little  waste.     Contains  the 
flank  steak.  Flank  meat  makes  excellent  pot  pie. 

5.  Round  —  A  juicy  cut,  free  from  fat.     The 
top  (or  inside)  is  used  for  steak  and    roasts. 
The  bottom  (or  outside)  is  best  chopped. 

6.  Rump  —  About  one-third  fat  and  one-half 
lean  meat.     Generally  used  for  steaks,  corning, 
braising  and  pot  roast. 

7.  Ribs  —  There  are  seven  ribs  in  this  cut. 
About  one-half  is  lean  meat,  one-third  fat  and 
one-sixth  bone.     The  two  ribs  nearest  the  loin 
make  excellent  roasts.    Ribs  are  always  roasted. 

8.  9,  10.  Loin  —  Contains  the  choicest  steaks  and  is  divided  into  two 
portions,  the  short  loin  and  the  loin  end.     This  latter  cut  contains  the 
sirloin,  pinbone  and  porterhouse  steaks. 

1 1 .  Clod  —  There  is  practically  no  waste  in  this  cut.      It  is  used  prin- 
cipally for  steaks  and  pot  roasts. 

12.  Brisket  —  Used  mostly  for  corned  beef;  also  used  for  soup,  pot 
roast  and  stew. 


FIG.  104.  A  side  of  beef. 
(Courtesy,  Wilson  and  Co.) 


204         FOODS  AND  HOW  WE  USE  THEM 

13.  Neck  —  Good  for  mince  meat;  also  as  a  brown  stew.  Flavor  and 
richness  are  added  by  cooking  with  salt  pork. 

Dangers  in  meat.  If  the  animals  themselves  are  unhealthy,  they  may 
contain  little  animals  in  their  flesh  which  can  enter  the  human  body  and 
produce  disease.  Tapeworms  come  from  beef.  Pork  may  contain  little 
"parasites"  which  produce  a  serious  disease.  The  protection  against 
these  is  to  cook  the  meat  thoroughly.  Inspection  of  all  meat  that  is  sold 
is  now  required.  Great  improvement  has  thus  been  brought  about  in 
recent  years  in  the  quality  of  meat. 

Other  diseases  are  due  to  bacteria  which  may  be  in  meat  which  has  been 
kept  too  long,  or  which  has  not  been  kept  thoroughly  chilled.  The  devel- 
opment of  improved  methods  of  cold  storage  and  of  refrigerator  cars  has 
done  wonders  in  making  it  possible  to  keep  meat  free  from  contamination. 

After  the  meat  has  been  brought  out  of  cold  storage,  however,  the  bac- 
teria which  may  have  been  in  it  all  the  time  are  given  a  chance  to  grow. 
New  bacteria  from  dust  and  flies  may  get  on  the  meat  and  develop  rapidly. 
Therefore  meat  should  be  used  as  soon  as  possible  after  having  been 
brought  from  cold  storage. 

Cleanliness  in  the  kitchen.  The  kitchen  should  be  the  cleanest 
room  in  the  house.  We  can  all  learn  lessons  from  great  bakeries 
and  even  slaughter-houses  in  regard  to  cleanliness.  Some  baker- 
ies require  that  every  employee  shall  wash  his  hands  on  returning 
to  the  room  after  leaving  it  for  any  purpose  whatever. 

"Food  and  fingers  are  carriers  of  contagion."  The  fingers 
which  handle  food  must  be  especially  clean.  Running  water, 
good  soap,  a  nail-brush  and  nail-cleaner  are  all  necessary  par.ts 
of  the  equipment  of  every  kitchen. 

Dishwashing,  the  bugbear  of  many  a  girl,  may  be  a  much  pleas- 
anter  and  much  cleaner  operation  than  it  usually  is.  A  bacteri- 
ologist calls  the  usual  way  of  washing  dishes  a  "  smear."  From 
what  you  have  learned  about  bacteria  and  their  dangers,  can  you 
not  see  how  important  it  is  to  be  immaculately  clean  about  the 
dishwashing? 

Use  plenty  of  hot  water  with  soap  or  washing  soda.  Change 
the  water  as  soon  as  it  becomes  at  all  greasy.  Rinse  the  dishes 
in  hot  water.  If  you  wipe  them,  use  a  clean  cloth.  A  better  and 
quicker  way  than  to  wipe  them  is  to  stack  the  dishes  in  a  good 
drainer  after  rinsing  and  pour  boiling  water  over  them.  They 
will  dry  by  evaporation  in  a  few  minutes. 


FOODS  IN  THE  HOME 


205 


NUMBER  of  BACTERIA  LEFT 
on  DISHES  after  DIFFERENT 

METHODS  ^WASHING 

•        Direct  rfiom.  tha  Table: 
57.000  Bacteria 
per  Auerafr  pirwer  Plate 


10500  Bacteria  ;aar  Plate 
fafaiM&BiSEc  GnsaiinJU 
,100  ;.  Bacteria,  per  Plate 


5.  OOP 
Washod.  fi 

1,400  &acteria/>er  Plate 


The  work  of  a  city  health  department.  An  organization  of  public- 
spirited  women  in  Boston  has  made  a  special  study  of  the  work  of  the  city 
departments  and  has  published  a  " Citizen's  Handbook"  in  which  the 

duties  of  the  government  of  their  city  are        

explained  in  simple  language.  Can  you 
find  out  how  many  similar  laws  your  city 
has? 

The  Health  Department  of  Boston  con- 
cerns itself  with  everything  which  has  to 
do  with  the  health  of  the  city.  It  makes 
regulations  about  the  sale  of  food,  the  care 
of  sickness  and  many  other  such  matters. 

It  has  made  a  regulation  which  forbids 
the  exposure  of  many  articles  of  food  to 
flies  and  to  the  dust  of  the  street.  There 
is  another  rule  which  says  that  all  places 
where  food  is  sold  and  all  people  who  sell 
it  must  be  clean  and  wholesome.  No 
room  in  which  food  is  kept,  prepared,  or 
sold  may  be  used  for  living  purposes. 
Newspapers  or  dirty  paper  must  not  be 
used  to  wrap  food  in. 

Milk  and  cream  which  are  for  sale  must 
be  kept  all  the  time  in  clean  refrigerators 
or  coolers. 

Milk  must  be  sold  in  tightly  closed 
bottles. 

No  person's  hands,  lips,  or  tongue  must  touch  milk  offered  for  sale. 

All  milk  bottles  must  be  washed  at  once  after  emptying  and  nothing 
else  must  be  kept  in  them. 

Pure  food  and  drug  laws.  Many  States  have  passed  pure  food 
and  drug  laws.  In  1906  Congress  passed  a  national  law.  These 
laws  relate  to  the  way  in  which  food  may  be  preserved.  It  is 
necessary  to  have  such  laws  because  some  manufacturers  in  pre- 
serving food  have  used  chemicals  which  have  a  harmful  effect  on 
the  body,  in  that  they  prevent  food  from  digesting  properly. 
Borax  or  boric  acid  make  spoiled  meat  appear  fresh.  Cheap 
sausages  are  apt  to  contain  such  meat.  Benzoate  of  soda  is  used 
in  many  canned  goods,  such  as  pickles  and  catsups.  The  law 
requires  that  if  such  preservatives  are  used,  their  names  shall 
appear  on  the  label.  Before  you  buy,  examine  the  labels  to  make 
sure  that  you  are  obtaining  pure  foovd. 


No  Bacteria.  Found  on.  Dishes 
Dished  &  QnsedinBoilirg  Water. 


FIG.  105.  Some  facts  about  dish- 
washing. 
(Courtesy,  Mothers'1  Magazine.) 


206          FOODS  AND  HOW  WE  USE  THEM 

INDIVIDUAL  PROJECTS 

Boys1  and  Girls'  Clubs: 

Canning  Clubs  and  Home  Economics  Clubs  may  be  formed  according  to  the 
suggestions  on  page  161. 

Camp-Fire  honors  in  Home  Craft  are  many.  How  many  can  you  earn  in  a 
week? 

Working  projects: 

1.  Make  a  loaf  of  bread.    All  the  girls  in  the  class  might  have  a  bread  contest, 
with  an  exhibition  at  school,  and  a  committee  of  mothers  to  judge  the  best 
loaves. 

2.  Make  a  card  catalogue  cookbook. 

This  may  be  along  certain  definite  lines: 
Bread  recipes  which  save  wheat. 
Conservation  desserts. 
The  favorite  dishes  of  the  class. 

3.  Make  an  investigation  of  the  food  stores  of  the  town  or  neighborhood. 
A  good  project  for  boys.     Make  a  score  card  for  each  store,  marking  for: 

Food  covered  or  not. 
Presence  of  flies. 
Neatness  of  arrangement. 
Appearance  of  employees,  etc. 

4.  Make  a  fly-trap.     See  reference  below. 

Reports: 

A  few  suggestive  subjects  are  named  below.  Others  may  appeal  to  you, 
after  reading  the  list  of  books  given  below,  and  working  out  the  problems  of  this 
project.  Use  the  library,  consult  town  and  state  authorities,  and  collect  ex- 
hibits for  your  work. 

1.  Dust  in  its  relation  to  food. 

2.  Flies  and  food. 

3.  How  my  town  protects  the  food  for  its  people. 

4.  Pure  food  laws  of  my  State. 

5.  The  life  and  work  of  Louis  Pasteur. 

6.  How  our  meat  reaches  us. 

7.  The  story  of  bread. 

8.  Harmful  preservatives  in  food. 

9.  Parasitic  insects  in  food. 

BOOKS  THAT  WILL  HELP  YOU 

Bacteria,  Yeasts  and  Molds  in  the  Home.     H.  W.  Conn.     D.  Appleton  &  Co. 

Non-technical,  with  many  suggestive  experiments. 
The  Book  of  Wonders.     Presbrey  Syndicate,  New  York. 

"The  Story  in  a  loaf  of  Bread." 

The  Cost  of  Cleanness.     E.  H.  Richards.    Wiley,  New  York. 
Dust  and  its  Dangers.     T.  M.  Prudden.    G.  P.  Putnam's  Sons,  New  York. 
Food  and  Health.     Kinne  and  Cooley.    The  Macmillan  Co. 

For  grammar  grades. 
Foods  and  Household  Management.     Kinne  and  Cooley.     The  Macmillan  Co. 

For  older  pupils. 

Household  Science  and  Arts.     May  Morris.    American  Book  Co. 
Wonders  of  Science.     E.  M.  Tappan,  Editor,    Houghton  Mifflin  Co. 

"How  Idaho  got  Pure  Food." 


FOODS  IN  THE  HOME  207 

Magazine  articles: 

Among  the  numerous  good  articles  may  be  mentioned 

"How  Bacteria  were  First  Seen."      Bowell.     Scientific  American  Supple- 
ment, March  4,  1916. 

"Modern  Bread-Baking."     Scientific  American,  March  II,  1916. 
Bulletins: 

Farmers'  Bulletins,  U.S.  Department  of  Agriculture: 
34.  Meats:  Composition  and  Cooking. 

128.  Eggs  and  their  Uses  as  Food. 

363.  The  Use  of  Milk  as  Food. 

375.  Care  of  Food  in  the  Home. 

413.  Care  of  Milk  and  Use  in  the  Home. 

459.  House- Flies. 

521.  Canning  Tomatoes  at  Home  and  in  Club  Work. 

839.  Canning  by  the  Cold-Pack  Method. 

841.  Drying  Fruits  and  Vegetables  in  the  Home. 
Extension  Circulars,  U.S.  Department  of  Agriculture: 

38.  Canning. 

32.  Evaporating. 
Publications  of  the  International  Harvester  Co.,  Chicago: 

Cold-Pack  Canning. 

The  Story  of  Bread. 

A  Home- Made  Fly -Trap. 
Health  Bulletins  of  the  Metropolitan  Life  Insurance  Co.,  New  York: 

All  about  Milk. 
Bulletins  of  the  University  of  Illinois: 

31.  Principles  of  Jelly- Making. 
Economy  in  the  Buying,  and  Preparation  of  Meats.   E.  L.  Wright.   Wilson  &  Co. 


PART  II.  MAN'S  CONTROL  OF  THE  FORCES  OF  NATURE 
INTRODUCTION  — THE  FORCES  OF  NATURE 

Law  of  cause  and  effect.  As  long  as  man  has  lived  upon  the 
earth  he  has  been  benefited  and  injured  by  the  operations  of  what 
are  commonly  called  the  forces  of  nature.  The  earth,  the  sunshine, 
and  the  rain  have  enabled  him  to  raise  his  crops  and  keep  himself 
and  his  domestic  animals  alive.  He  has  made  fires  to  help  him 
prepare  his  foods  and  to  keep  himself  warm.  He  has  learned  how 
in  many  ways  to  use  the  force  of  the  wind  and  water.  At  the 
same  time  he  has  often  witnessed  and  suffered  from  the  terrible 
effects  of  storms  and  floods.  He  has  experienced  the  extreme 
heat  of  summer  and  the  awful  cold  of  winter.  He  has  seen  the 
devastating  destruction  of  fire.  He  has  been  the  victim  of  earth- 
quakes and  volcanoes. 

Man  is  different  from  other  animals  in  that  he  has  the  ability 
to  think  and  reason.  The  ways  in  which  half -civilized  man  tried 
to  explain  the  causes  for  the  existence  of  natural  phenomena  are 
far  removed  from  the  true  explanations.  Yet  the  fact  that  he 
realized  the  need  of  some  explanation  for  these  events  indicates 
that  even  at  that  time  he  was  dimly  conscious  of  a  great  funda- 
mental law  of  nature  which  we  call  the  law  of  cause  and  effect. 

As  far  as  our  knowledge  extends,  an  event  never  happens  with- 
out a  natural  cause.  We  have  yet  to  find  a  single  instance  of 
anything  taking  place  without  a  force  or  cause  producing  it. 
Things  do  not  "just  happen."  They  happen  because  a  certain 
train  of  circumstances  makes  them  happen.  This  is  what  is 
meant  by  the  law  of  cause  and  effect. 

Early  explanations  of  natural  phenomena.  Although  semi- 
civilized  man  realized  the  necessity  of  believing  that  an  effect 
implies  a  cause,  he  "was  unable,  because  of  his  ignorance,  to  assign 
correct  explanations  for  many  of  the  most  common  occurrences 
taking  place  around  him.  Usually  he  attempted  to  explain  them 


THE  FORCES  OF  NATURE       209 

by  supposing  that  spirits  caused  them.  This  kind  of  explanation 
appealed  to  him  because  it  was  simple  and  did  not  require  much 
thinking.  He  usually  pictured  to  himself  good  and  evil  spirits, 
and  much  of  his  time  was  spent  in  doing  what  he  believed  would 
be  pleasing  to  the  spirits  which,  he  thought,  controlled  the  forces 
of  nature,  as  well  as  the  very  existence  of  living  beings. 

In  certain  regions  of  the  world  such  beliefs  are  still  to  be  found. 
Thus,  in  some  parts  of  Burma  altars  are  built  near  springs  to 
keep  the  spirit  of  the  spring  in  good  humor  so  that  the  water  may 
be  pure  and  cold.  If  the  spring  runs  dry  or  some  one  gets  sick 
from  drinking  the  water,  the  natives  believe  that  it  is  because  the 
guardian  spirit  of  the  spring  has  been  offended.  The  remedy 
consists  in  offering  some  sacrifice  to  the  spirit.  This  is  a  typical 
illustration  of  the  way  in  which  in  the  past  some  common  events 
have  been  explained. 

It  is  unnecessary,  however,  to  go  to  Burma  to  find  instances 
of  superstition.  There  are  many  superstitious  beliefs  that  are 
accepted  by  some  so-called  educated  people  of  our  own  land. 
For  example,  some  persons  believe  that  finding  a  horseshoe  brings 
"  good  luck,"  breaking  a  mirror  "  hard  luck,"  and  "  knocking  on 
wood  "  prevents  harm.  Our  science  work  ought  to  teach  us  very 
clearly  that  such  ideas  are  foolish,  and  that  events  do  not  happen 
without  a  natural  cause.  If  we  do  not  know  in  any  particular 
case  just  why  a  certain  effect  has  been  produced,  let  us  by  all 
means,  as  educated  people,  be  absolutely  certain  that  it  is  the 
result  of  natural  law. 

Man's  control  of  the  forces  of  nature.  In  this  second  part  of 
our  study  of  the  science  of  everyday  life  we  are  to  learn  something 
of  the  great  forces  which  rule  our  world.  We  must  know  about 
the  forms  of  energy  which  exist  about  us,  and  how  man  has 
learned  to  use  them,  in  lighting  and  heating  his  homes,  and  in 
transporting  him  from  place  to  place.  We  must  know  something 
about  the  relationship  between  the  many  forms  of  energy  and 
the  sun,  the  source  of  all  the  energy  upon  the  earth. 

Matter  and  energy.  In  order  even  to  begin  to  understand  about 
the  operation  of  the  forces  of4  nature,  we  must  first  know  that  the 
world  and  everything  in  it  are  composed  of  three  forms  of  matter 


210  THE  FORCES  OF  NATURE 

—  solids,  liquids,  and  gases.  (See  page  8.)  Whenever  any- 
thing happens  to  any  materials  or  substances  in  our  world  so  as 
to  make  them  change  their  relative  positions  one  to  another  or 
change  their  forms,  we  may  be  sure  that  such  events  are  brought 
about  through  the  agency  of  some  form  of  energy. 

By  energy  is  meant  the  capacity  to  perform  work.  The  word 
"  work  "  in  this  connection  not  only  applies  to  what  man  does,  but 
it  includes  the  results  of  the  actions  of  what  we  have  called  the 
forces  of  nature.  It  is  impossible  to  study  energy  except  in  con- 
nection with  matter.  This  is  true  because  matter  and  energy 
react  closely  and  completely  with  each  other.  It  is  upon  this 
action  and  interaction  of  matter  that  the  law  of  cause  and  effect 
depends. 

In  our  study  of  air  and  water,  some  time  was  spent  in  learning 
about  their  possible  effects  when  in  motion.  Motion  is  not  ma- 
terial. It  is  a  form  of  energy.  We  have  referred  to  light  and  heat 
in  connection  with  oxidation  and  to  the  fact  that  electricity  may 
be  generated  by  harnessing  the  power  of  falling  water.  Heat, 
light,  and  electricity  are  not  matter.  They  are  forms  of  energy. 
It  is  impossible  to  purchase  a  barrel  of  heat,  light,  motion,  or 
electricity  as  you  can  buy  some  materials.  Just  what  these  forms 
of  energy  are  nobody  as  yet  has  been  able  exactly  to  tell,  although 
there  are  theories  about  them.  We  know  that  they  exist  because 
we  can  see  their  effects.  They  can  best  be  described  by  stating 
the  effects  which  they  are  capable  of  producing  upon  matter. 
Thus,  we  have  noted  the  fact  that  oxidation,  one  of  the  most 
common  kinds  of  change,  is  brought  about  through  the  agency 
of  heat.  We  have  noted  that  water  may  be  made  into  an  in- 
visible gas  by  the  application  of  heat.  We  have  found  that 
electricity  will  produce  a  change  in  water,  making  it  decompose 
into  its  elements,  hydrogen  and  oxygen.  Light  also  is  able  to 
produce  changes  in  many  substances,  such  as  upon  sensitized 
films  and  photographic  paper,  thus  making  it  possible  to  take 
pictures.  These,  of  course,  are  only  a  few  of  multitudes  of  illus- 
trations which  might  be  cited  to  show  that  the  different  forms  of 
energy  produce  changes  in  the  materials  of  which  our  world  is 
made. 


THE  FORCES  OF  NATURE 


211 


The  energy  of  living  beings.  Ever  since  very  early  times 
man  has  made  use  of  the  energy  possessed  by  other  animals  to 
help  in  doing  work.  One  of  the  earliest  animals  to  be  domes- 
ticated was  the  dog,  which  is  supposed  to  be  descended  from 
the  wolf.  The  work  of  ex- 
plorers in  the  Arctic  and  Ant- 
arctic regions  has  been  de- 
pendent on  the  dogs,  which 
have  in  some  cases  such  stores 
of  energy  that  they  are  able  to 
draw  a  heavily  loaded  sledge 
ten  successive  days  without 
food.  Horses,  oxen,  donkeys, 
elephants,  and  camels  have 
long  been  used  by  man  to 
help  him  in  his  work. 

Plants,  too,  possess  an  enor- 
mous amount  of  energy.  Roots 


^BfO 


r 


FIG.  106.  At  the  south  pole,  thanks  to  the 

energy  of  the  dogs. 
(Copyright,  Underwood  and  Underwood.) 


of  plants  accomplish  a  great 
amount  of  work  in  loosening  the  soil.  A  huge  boulder  may  often 
be  seen  to  be  split  in  two  by  the  pressure  of  a  root  which  is 
forced,  wedge-like,  into  a  crack  in  the  rock.  Do  you  wonder  how 
living  creatures  obtain  all  this  energy?  Food  is  the  energy-maker. 
In  all  living  creatures  food  serves  the  same  purpose;  it  is  used  to 
build  the  cells,  or  it  is  oxidized  to  furnish  energy.  (See  page  168.) 

Energy  possessed  by  inanimate  objects.  Can  work  be  done 
except  by  living  beings?  If  you  have  ever  seen  Niagara  Falls 
you  were  impressed  by  the  roar  of  the  immense  volume  of  water 
as  it  falls  over  the  brink  and  strikes  the  broken  rocks  below.  Per- 
haps you  have  been  behind  the  Falls,  deafened  by  the  noise, 
speechless  with  the  thought  of  the  great  power  such  a  mass  of 
water  can  exert.  Only  a  small  amount  of  the  water  from  the 
Falls  is  used  at  present,  but  it  is  estimated  that  this  one  cataract 
is  capable  of  furnishing  seven  million  horse-power,  day  and  night. 
In  other  words,  it  can  do  as  much  work  in  an  hour  as  seven  million 
horses  can. 

During  one  day  of  the  battle  of  the  Somme,  the  artillery  alone 


212  THE  FORCES  OF  NATURE 

used  fifteen  million  pounds  of  gunpowder.  Every  pound,  when 
it  exploded,  increased  in  volume  at  least  three  hundred  times. 
Yet  the  gases  from  the  gunpowder  were  not  free  to  spread  in  all 
directions;  they  were  confined  in  cannon,  guns,  and  machine 
guns.  Can  you  picture  the  work  that  was  done  by  that  expand- 
ing powder  as  it  hurled  bullets  and  shells  against  the  enemy? 

These  two  examples  are  enough  to  make  you  realize  that  energy 
is  not  confined  to  living  bodies.  Examples  of  inanimate  objects 
possessing  energy  are  on  every  hand,  as  the  molten  rock  in  a 
volcano,  the  speeding  submarine,  the  cannon  ball,  the  gasoline 
in  the  automobile  tank. 

The  energy  of  motion  —  kinetic  energy.  A  bowler  imparts 
energy  to  the  ball  that  he  sends  down  the  alley.  It  strikes  the 
pins  with  such  force  that  they  fall  with  a  crash.  One  pin  hits 
another,  knocking  it  down.  While  the  ball  rests  in  the  runway 
and  while  the  pin  stands  in  its  place  they  have  no  energy  them- 
selves. Only  while  they  are  moving  do  they  possess  the  energy  to 
accomplish  work. 

Moving  air  has  enough  energy  to  cause  windmills  to  turn,  and 
to  carry  great  ships  around  the  world.  Sometimes  its  force  is  so 
great  that  instead  of  being  an  agent  of  good,  accomplishing  much 
of  the  work  of  the  world,  it  becomes  an  agent  of  destruction. 
Storms  known  as  typhoons,  accompanied  by  high  winds,  visit 
certain  parts  of  the  globe.  In  1906  Hongkong  was  visited  by 
such  a  storm,  which  destroyed  five  thousand  lives  and  twenty 
million  dollars'  worth  of  property.  Have  you  known  of  havoc 
wrought  by  high  winds? 

An  automobile,  a  toboggan,  a  tennis-ball,  the  piston  in  an 
engine,  all  possess  energy  when,  and  only  when,  they  are  in  mo- 
tion. This  kind  of  energy  is  known  as  kinetic  energy,  or  the  energy 
of  motion.  The  earth  itself,  as  it  moves  through  space,  possesses 
an  enormous  amount  of  kinetic  energy. 

Stored-up  energy  —  potential  energy.  A  lifted  hammer  falls 
on  a  nail  with  enough  force  to  drive  it  into  the  board ;  a  huge  iron 
44  skull-cracker"  is  dropped  on  granite  boulders  with  enough  force 
to  crush  them;  a  watch-spring  is  wound  into  a  tight  coil  which 
turns  the  wheels  in  the  works  as  it  uncoils.  These  are  examples 


THE  FORCES  OF  NATURE 


213 


of  energy  stored  up  because  of  the  position  of  the  object.  All 
bodies  which  possess  stored  up  energy  are  capable  of  doing  work 
only  when  the  energy  is  released. 

Forms  of  energy.  One  form  of  energy  is  heat.  Heat  can  do 
work,  as  we  well  know.  It  can  cause  water  to  expand  to  steam; 
it  can  raise  the  mercury  in  a  thermometer;  it  can  start  a  fire. 

The  food  in  the  world  is  produced  by  another  form  of  energy, 
that  of  light.  In  the  tiny  cells  of  plants  lies  the  machinery  run 
by  the  energy  of  light,  the  microscopic  chloroplasts  which  change 
the  raw  materials,  carbon  dioxide  and  water,  into  valuable  foods 
for  the  world.  (See  pages  157-159.)  To  the  energy  of  light,  too, 
we  owe  our  photographs.  Work  is  done  when  the  silver  salts  are 
changed  by  the  action  of  light,  producing  on  the  plate  the  shad- 
ows and  lights  of  the  negative. 

Imagine  the  modern  world  without  electricity.  How  many  of 
your  common  conveniences  and  pleasures  are  due  to  it?  Work 
done  by  electrical  energy  is  the  most  startling  and  wonderful  of  all 
work.  By  it  messages  are  sent  in  lightning  time  from  continent 
to  continent;  by  it  the 
power  of  a  Niagara  can 
drive  factories  and  trolley 
cars  in  distant  cities. 

A  shell  hurled  from  a 
cannon  owes  its  destruc- 
tive force  not  only  to  the 
energy  of  motion  that  it 
has,  but  to  the  chemical 
energy  of  its  charge.  When 
it  explodes,  the  contents 
produce  gases  which  oc- 
cupy vastly  more  space  than  the  shell  itself,  and  scatter  de- 
struction over  a  wide  area.  Other  examples  of  chemical  energy 
are  shown  in  baking  powder,  which  is  able  to  make  a  cake  rise; 
in  the  contents  of  a  fire  extinguisher,  which  can  throw  a  stream 
of  stifling  gas  on  a  fire ;  and  in  acids  which  can  eat  their  way 
through  cloth,  wood,  and  human  flesh. 

Energy  may  change  its  form.     Several  instances  have  already 


FIG.  107.  A  bursting  shell. 
(Copyright,  Western  Newspaper  Union.) 


214  THE  FORCES  OF  NATURE 

been  given  where  energy  changes  its  form  or  is  transformed.  Let 
us  briefly  consider  two :  (i)  Water  power  may  be  used  to  run  dyna- 
mos to  generate  electricity.  (2)  Coal  may  be  burned  and  the 
heat  thus  produced  may  be  used  to  run  dynamos  to  generate 
electricity.  In  the  first  place,  electrical  energy  is  obtained  from 
the  motion  energy  of  falling  water.  In  the  second  case,  electrical 
energy  is  obtained  from  the  heat  energy  from  the  burning  coal. 
This  electrical  energy  may  be  transformed  back  again  into  heat, 
as  is  done  in  the  case  of  electric  irons.  It  may  be  transformed 
into  motion  by  the  electric  motor  or  into  light  by  the  electric  light 
bulb. 

Energy  can  never  be  made  from  nothing.  We  have  seen  that 
just  as  matter  may  be  transformed  (see  page  32),  so  may  energy 
be  transformed.  Just  as  matter  cannot  be  made  from  nothing 
(see  page  33),  likewise  energy  cannot  come  into  existence  unless 
there  was  energy  present  in  the  first  place.  If  the  water  ceases 
to  flow  or  the  fires  are  extinguished  at  the  power-station,  elec- 
tricity is  no  longer  generated.  Furthermore,  the  amount  of  elec- 
tricity which  can  be  generated  is  limited  by  the  amount  of  energy 
that  is  present  in  the  falling  water  or  in  the  coal. 

Energy  cannot  be  destroyed.  The  third  great  law  regarding 
energy  is  that  although  energy  may  be  dissipated  or  wasted,  none 
of  it  can  be  destroyed.  Energy  is  indestructible.  In  this  respect, 
also,  energy  is  like  matter.  (See  page  32.)  Thus,  the  motion  of 
a  steam  engine  may  be  only  twenty  per  cent  of  the  total  amount 
of  energy  in  the  coal  that  is  used  to  run  the  machine.  The  other 
eighty  per  cent  is  not  destroyed.  It  has  gone  to  heat  surrounding 
objects  instead  of  actually  entering  into  the  motion  of  the  ma- 
chine. Again  the  light  from  an  electric  bulb  may  be  less  than 
eight  per  cent  of  the  total  amount  of  energy  in  the  coal  that  must 
be  burned  to  produce  the  light.  Most  of  the  remaining  energy  is 
transformed  into  heat.  A  fundamental  and  absolutely  true  con- 
ception regarding  energy  is  this:  As  far  as  man's  knowledge  ex- 
tends there  is  just  as  much  energy  in  the  universe  to-day  as  there 
always  has  been,  and  there  always  will  be  as  much  as  there  is 
to-day. 

Some  common  sources  of  energy.     We  have  just  referred  to 


THE  FORCES  OF  NATURE       215 

two  of  the  most  common  sources  of  energy;  namely,  waterfalls 
and  coal.  It  has  also  previously  been  pointed  out  that  the  body 
needs  food  for  its  energy.  We  are  accustomed  as  soon  as  we 
hear  the  word  coal  to  think  of  heat.  When  oil  or  illuminating  gas 
is  mentioned,  we  are  apt  to  think  of  light.  When  gasoline  is 
referred  to,  we  think  of  the  moving  automobile,  motor  boat,  or 
airplane.  Similarly  when  the  word  food  is  mentioned,  it  should 
call  to  mind  the  fact  that  from  it  we,  and  all  other  living  things, 
obtain  the  power  to  carry  on  life  activities. 

It  has  been  through  a  long  period  of  experimentation,  which  is 
still  going  on,  that  it  has  been  discovered  that  certain  things  in 
or  upon  the  earth  have  energy  stored  in  them.  The  first  experi- 
ments with  such  things  must  have  been  more  or  less  accidental. 
Thus,  before  any  one  knew  anything  about  coal,  we  can  imagine 
the  surprise  of  a  savage  upon  discovering  that  what  he  must  have 
considered  a  black  rock  would  burn  when  heated.  Likewise,  all 
our  articles  of  food  must  have  been  experimented  with  before 
their  value  as  energy-givers  could  have  been  determined. 

Conserving  nature's  storehouse  of  energy.  The  amount  of 
energy  on  the  earth  is  limited.  We  have  found  that  the  great 
source  of  the  energy  of  living  beings  is  their  food.  Fertile  soils 
capable  of  growing  food  are  valuable  and  must  not  be  wasted. 
Our  great  sources  of  heat  are  coal,  wood,  and  oil.  During  the 
past  century  we  have  been  using  the  supply  of  these  substances 
much  more  rapidly  than  nature  has  been  able  to  replace  .them. 
The  amount  of  energy  in  running  water  depends  upon  the  volume 
of  water.  If  we  allow  our  streams  to  dry  up,  as  may  be  done  by 
ruthlessly  cutting  down  the  forests  near,  we  are  wasting  a  great 
store  of  energy.  As  the  population  of  the  earth  increases,  and 
as  these  great  forces  of  nature  are  used  more  and  more  to  accom- 
plish the  work  of  the  world,  nations  are  finding  it  necessary  to 
pass  laws  to  insure  the  conservation  of  our  natural  resources. 

Original  source  of  all  energy  upon  the  earth.  If  it  is  true,  as 
has  been  stated,  that  energy  cannot  come  from  nothing,  it  is  evi- 
dent that  running  water,  coal,  wood,  food,  etc.,  must  have  ob- 
tained their  energy  from  some  source  or  sources  of  supply. 

The  energy  of  running  water  is  due  to  its  position.    Therefore, 


2l6 


THE  FORCES  OF  NATURE 


if  we  find  out  how  it  came  to  be  in  an  elevated  position,  we  shall 
discover  the  source  of  its  energy.  As  we  have  already  found  out 
in  a  previous  project,  the  sun  lifts  the  water  above  the  surface  of 
the  earth  in  the  form  of  an  invisible  vapor.  Then  it  is  condensed 
and  returns  to  the  earth  in  liquid  or  solid  form.  Much  of  it  again 
reaches  the  streams  and  helps  to  make  it  possible  for  them  to  do 
work. 

The  sun  is  necessary  for  plant  growth.  Since  all  food  and  fuel 
come  either  directly  or  indirectly  from  plants,  the  importance  of 
the  sun  in  this  connection  can  readily  be  seen.  In  fact,  the 
energy  in  fuel  and  food  is  correctly  termed  bottled  sunlight,  and 
every  act  of  man  is  in  truth  a  transformed  sunbeam. 

The  sun  and  other  stars.  Our  sun  is  really  a  star,  smaller  than 
many  other  stars.  The  reason  that  the  sun  looks  so  large  and  the 
stars  so  small  is  because  the  sun  is  only  93,000,000  miles  away, 
whereas  the  nearest  star  to  us  is  several  million  times  this  dis- 
tance from  us.  All  the  stars,  including  the  sun,  shine  by  reason 
of  their  own  light  and  not  by  light  that  is  reflected  from  some 
other  source,  as  is  the  case  with  the  moon.  It  takes  the  light  from 
the  sun  eight  minutes  to  reach  us;  that  is  to  say,  light  travels  at 
the  rate  of  186,000  miles  a  second.  Notwithstanding  this  great 
speed,  it  takes  the  light  from  the  nearest  star  over  four  years  to 

reach  us,  and  some  stars 
are  so  far  away  that  if 
they  were  to  go  out  of  ex- 
istence to-day,  the  people 
upon  the  earth  would  not 
know  of  it  for  hundreds 
of  years  because  the  light 
from  them  takes  that 
length  of  time  to  reach 
us. 


FIG.  108.  The  Big  Dipper  and  the  North  Star. 
(From  Clarke's  Astronomy  from  a  Dipper.) 


Constellations.  Groups 
of  stars  are  known  as  con- 
stellations. Ancient  peoples,  looking  up  into  the  heavens,  imagined 
that  the  stars  were  arranged  in  certain  groups  so  as  to  represent 
various  things,  such  as  dragons,  wild  animals,  great  heroes,  and 


THE  FORCES  OF  NATURE 


217 


various  objects.  The  names  which  have  been  given  to  groups 
of  stars  have  been  handed  down  to  us  and  are  still  used.  Thus, 
we  speak  of  the  "  Great  Bear  "  and  the  "  Little  Bear,"  two  con- 
stellations that  can  be  seen  in  the  heavens  at  all  times  of  the 
year.  They  are  situated  near  the  north  star.  In  fact,  the  north 
star  or  pole  star  helps  to  form  the  latter  constellation. 

The  north  star.  The  north  star,  because  it  has  been  used  from 
time  immemorial  to  point  out  direction  both  to  mariners  and  to 
those  traveling  over  the  land,  is  probably  the  best-known  star  in 
the  heavens.  All  the  other  stars  seem  to  revolve  around  it.  That 
is  because  it  is  almost  in  a  direct  line  with  the  north  pole  of  the 
earth,  or,  more  correctly  stated,  it  is  in  line  with  the  earth's  axis. 
It  is  possible  by  first 
locating  the  north  star 
to  find  rather  easily 
many  of  the  constella- 
tions. In  order  to  find 
the  star,  look  into  the 
northern  sky  at  any  time 
of  the  year  on  a  clear 
night.  Locate  the  big 
dipper.  The  two  stars 
which  make  the  sides  of 
the  bowl  farthest  re- 
moved from  the  handle 
together  constitute  what 
are  called  the  pointers. 
These  stars  have  been 
given  this  name  because 
they  point  almost  di- 
rectly to  the  north  star. 
This  star  is  of  about 
equal  brilliancy  to  the 

pointers  and  about  five  times  as  far  away  from  them  as  the 
distance  between  these  two  stars. 

The  solar  system.    How  different  is  our  knowledge  about  the 
sun  and  stars  from  that  possessed  by  ancient  peoples!     It  was 


FIG.  109.  The  solar  system.  The  large  planets  in 
order  of  their  distance  from  the  sun  are  Mercury, 
Venus,  the  Earth,  Mars,  Jupiter,  Saturn,  Uranus, 
and  Neptune.  Between  Mars  and  Jupiter  are  sev- 
eral small  bodies  called  planetoids.  A  comet  and  its 
orbit  is  also  shown.  Find  the  satellites  or  moons 
which  move  around  the  planets. 


218  THE  FORCES  OF  NATURE 

formerly  thought  that  the  sun  was  a  chariot  of  fire  driven  across 
the  heavens,  which  were  a  kind  of  canopy  in  which  the  gods 
placed  lamps  at  night,  and  that  the  earth  was  the  center  of  the 
universe.  Now  we  know  that  the  earth  is  really  only  a  very  tiny 
body  of  matter  among  all  the  other  worlds  and  stars,  and  that 
it  and  seven  other  heavenly  bodies  called  planets  revolve  around 
the  sun.  The  sun  and  these  bodies  with  lesser  ones  which  in  turn 
revolve  around  them  make  up  what  is  known  as  the  solar  system. 
The  word  solar  means  sun,  and  it  is  very  likely  that  the  stars, 
which  are  really  suns,  have  bodies  revolving  around  them. 


FIG.  no.  Phases  of  the  moon.  The  moon  is  shown  in 
eight  different  positions  in  its  orbit  around  the  earth.  The 
side  turned  toward  the  sun  is  light.  The  appearance  of  the 
moon  as  we  see  it  from  the  earth  is  shown  by  the  inner 
figures.  (The  comparative  sizes  of  the  earth,  moon,  and 
sun,  and  of  the  orbits  of  moon  and  earth  are  not  in  correct 
proportion.) 

When  we  think  of  some  of  these  things,  we  are  amazed  and 
dumfounded.  Comparing  the  size  of  the  earth  with  that  of  the 
sun,  we  find  that  the  earth's  diameter  is  only  8000  miles,  while 
that  of  the  sun  is  800,000  miles.  The  planets  are  eight  in  num- 
ber and  their  names  are,  in  order  of  their  size,  Mercury,  Mars, 
Venus,  Earth,  Uranus,  Neptune,  Saturn,  and  Jupiter.  Mer- 


THE  FORCES  OF  NATURE  219 

cury,  besides  being  the  smallest,  is  also  the  nearest  to  the  sun, 
being  36,000,000  miles  distant.  Neptune  is  farthest  from  the 
sun,  being  3,000,000,000  miles  away. 

Moons.  Most  planets  have  bodies  of  their  own  which  revolve 
around  them.  The  earth,  as  we  know,  has  one  such  body,  called 
the  moon.  Neptune  has  eight  and  Saturn  ten.  Our  moon  has 
no  atmosphere  or  air  about  it,  and  always  keeps  the  same 
surface  turned  toward  us.  No  one  has  seen  but  one  side  of 
the  moon.  We  say  the  moon  is  full  at  certain  times;  a  crescent 
at  other  periods,  and  a  new  moon  at  still  other  times.  The 
moon  shines  by  reflected  light  from  the  sun,  and  naturally  we 
see  only  that  part  of  its  surface  upon  which  the  sun  is  shin- 
ing. The  illustration  on  page  218  will  help  to  make  this  point 
clear. 

Years.  All  of  the  planets  revolve  around  the  sun,  the  time 
necessary  for  a  complete  revolution  making  what  we  call  a  year. 
The  lengths  of  these  years  differ  for  different  planets.  Thus,  as 
compared  with  the  earth,  Mercury  has  a  year  of  only  three 
months'  duration  while  Neptune's  year  is  equal  to  one  hundred 
and  sixty-five  of  ours. 

Seasons.  Our  seasons  are  due  to  four  causes :  the  revolution  of 
the  earth  around  the  sun  each  year,  the  rotation  of  the  earth  on  its 
own  axis  once  every  twenty-four  hours,  the  inclination  or  tip- 
ping of  the  axis  of  the  earth  23  1/2  degrees  from  the  perpendicu- 
lar and  the  fact  that  the  axis  always  points  in  the  same  direc- 
tion, and  the  spherical  shape  of  the  earth.  Only  at  two  short 
periods  in  the  year,  known  as  the  spring  equinox,  March  2ist,  and 
the  autumnal  equinox,  September  22d,  do  the  perpendicular  rays 
of  the  sun  fall  directly  on  the  equator.  On  those  dates  day  and 
night  are  equal  in  length  everywhere  on  the  earth.  From  the 
date  of  the  spring  equinox  to  the  autumnal  equinox  the  northern 
hemisphere  is  inclined  toward  the  sun,  and  the  southern  hemi- 
sphere away  from  the  sun.  There  is  no  night  in  all  this  time 
at  the  north  pole,  and  no  day  at  the  south  pole,  and  the  days 
are  longer  than  the  nights  in  all  the  northern  hemisphere.  The 
longest  day  in  the  northern  hemisphere  is  the  date  of  the  summer 
solstice,  June  2ist.  On  this  date  the  perpendicular  rays  of  the 


220  THE  FORCES  OF  NATURE 

sun  fall  on  the  Tropic  of  Cancer,  which  is  23  1/2  degrees  north 
of  the  equator.  When  the  rays  of  the  sun  are  more  nearly  per- 
pendicular, and  the  days  are  longer  than  the  nights,  we  receive 


FIG.  in.  A  diagram  to  show  the  causes  of  the  seasons.  The  north  pole  is 
visible  in  each  position.  How  far  do  the  rays  of  the  sun  reach  each  month? 
Demonstrate  the  reason  for  the  change  of  seasons,  using  a  globe.  The  earth's 
orbit  is  not  a  perfect  circle,  but  an  ellipse.  The  earth  is  slightly  nearer  the  sun 
at  the  time  of  perihelion  about  January  i  than  at  the  time  of  aphelion  about 
July  i. 

greater  heat,  and  we  call  the  season  summer.  Summer  in  the 
northern  hemisphere  is  winter  in  the  southern  hemisphere. 

Day  and  night.  The  earth  rotates  constantly  on  its  axis,  so 
only  one  half  the  earth  can  receive  the  direct  rays  of  the  sun  at  a 
time,  and  consequently  night  and  day  follow  each  other. 

The  length  of  day  and  night  varies  with  the  distance  from  the 
equator.  At  the  equator  the  day  is  always  twelve  hours  long  and 
the  night  twelve  hours  long.  The  poles  have  a  six-months  day 
and  a  six-months  night.  Between  these  two  extremes  the  length 
of  day  and  night  varies. 

Most  of  the  other  planets,  besides  revolving  around  the  sun, 


THE  FORCES  OF  NATURE  221 

also  rotate  on  their  own  axes.  The  lengths  of  the  days  and  nights 
differ  for  different  planets.  Jupiter  rotates  on  its  axis  at  the 
approximate  rate  of  once  every  ten  hours.  Its  days  and  nights 
are  therefore  only  five  hours  long.  Venus,  which  rotates  on  its 
axis  only  once  during  its  revolution  around  the  sun,  has  per- 
petual day  on  one  half  of  its  surface  and  perpetual  night  on  the 
other  half. 

Time.  It  was  formerly  the  custom  for  every  one  to  tell  time  by 
the  sun.  The  moment  when  the  sun  was  most  nearly  overhead 
at  any  place  was  called  noon.  This  was  very  inconvenient  be- 
cause of  a  lack  of  uniformity.  Especially  after  the  railroads  and 
telegraphs  were  built,  this  method  of  telling  time  was  undesir- 
able. In  1883  the  United  States  Government  decided  to  estab- 
lish time  belts.  They  are  called  Eastern,  Central,  Mountain,  and 
Pacific  time.  The  country  is  divided  into  the  four  sections  as 
shown  in  the  diagram,  each  belt  to  the  west  having  one  hour 
later  time  than  the  belt  immediately  adjoining  it  to  the  east. 
Thus,  when  it  is  twelve,  noon,  in  New  York  it  is  eleven  o'clock 
in  Chicago,  ten  o'clock  in  Denver,  and  nine  o'clock  in  San  Fran- 
cisco. When  it  is  four  o'clock  in  the  afternoon  in  Portland, 
Maine,  what  time  is  it  in  Portland,  Oregon?  (See  figure  112.) 

Gravitation.  Almost  every  one  has  heard  the  story  of  Sir  Isaac 
Newton.  It  is  said  that  as  he  sat  one  day  under  an  apple  tree 
he  was  hit  on  the  head  by  a  falling  apple  and  thus  was  set  to 
thinking  about  why  the  apple  fell  toward  the  ground.  As  a  re- 
sult of  his  thinking  upon  this  problem  he  was  eventually  able 
to  formulate  certain  great  truths  which  no  one  before  his  time  had 
been  able  to  do.  Many  people,  of  course,  before  him  had  seen 
apples  and  other  objects  fall  to  the  ground,  but  no  one  had 
thought  very  much  about  the  reason.  Like  many  other  common 
events  this  one  had  been  taken  for  granted.  Sir  Isaac  Newton, 
however,  saw  in  such  a  common  event  as  a  falling  apple  the  heart 
of  a  great  problem.  Sometime,  perhaps,  you  will  study  the  sub- 
ject called  physics,  and  then  you  will  learn  about  the  laws  of  gravi- 
tation. In  brief,  we  know  that  there  is  an  attractive  force  exist- 
ing between  all  the  different  objects/great  and  small,  that  com- 
pose the  universe.  When  the  attraction  is  exerted  by  the  earth 


THE  FORCES  OF  NATURE  223 

we  call  that  special  force  gravity.  It  is  that  force  which  tends  to 
pull  all  objects  on  the  earth  toward  its  center.  Thus,  objects  fall 
to  the  ground  because  of  the  force  of  gravity. 

Although  it  is  200,000  miles  away,  the  moon  is  near  enough  to 
the  earth  to  be  influenced  by  gravity.  In  fact,  the  moon  revolves 
about  the  earth,  because  it  is  held  in  its  orbit  by  this  force.  The 
moon  also  exerts  an  attractive  pull  upon  the  earth,  but  the  earth's 
pull  upon  the  moon  is  greater  because  the  earth's  mass  is  greater 
than  the  moon's.  Our  tides  are  almost  entirely  caused  by  the 
influence  of  the  moon.  Since  water  is  more  easily  moved  and 
piled  up  than  land,  some  of  it  is  actually  heaped  up  at  certain 
places  and  drawn  away  from  other  places,  producing  the  rising 
and  falling  of  the  tides. 

Not  only  is  the  moon  held  in  place  by  this  great  force,  gravita- 
tion, but  the  same  force  holds  the  sun  and  the  planets  in  their 
relative  positions.  The  earth  and  the  other  planets  are  kept  in 
their  orbits  and  move  through  space  by  the  force  of  gravitation. 
Indeed,  the  motions  of  the  stars  and  their  systems  are  all  con- 
trolled by  gravitation.  Sir  Isaac  Newton,  whose  wonderful  mind 
was  the  first  to  grasp  the  true  meaning  of  these  commonly  ob- 
served phenomena,  said,  "  I  do  not  know  what  I  may  appear  to 
the  world,  but  to  myself  I  seem  to  have  been  only  like  a  boy  play- 
ing on  the  seashore  and  diverting  myself  now  and  then  finding  a 
smoother  pebble  or  a  prettier  shell  than  the  ordinary,  whilst  the 
great  ocean  of  truth  lay  all  undiscovered  before  me." 

INDIVIDUAL  PROJECTS 

Working  projects: 

I.  Learn  to  recognize  a  few  constellations. 

The  Book  of  Stars.     A.  F.  Collins.     D.  Appleton  &  Co. 
Earth  and  Sky  Every  Child  Should  Know.     J.  E.  Rogers.     Doubleday, 
Page  &  Co. 

Reports: 

1.  Life  and  work  of  Sir  Isaac  Newton. 

The  Story  of  Great  Inventors.     F.  E.  Burns.     Harper  &  Bros. 

2.  Interesting  facts  about  the  stars  and  planets. 

The  Children's  Book  of  Stars.     G.  A.  Mitton.     Adam  and  Chas.  Black, 

London. 

The  Friendly  Stars.     M.  E.  Marten.     Harper  &  Bros. 
The  Stars  and  Their  Stories.     A.  M.  M.  Griffith.     Henry  Holt  &  Co. 
The  Ways  of  the  Planets.     M.  E.  Marten.     Harper  &  Bros. 


224  THE  FORCES  OF  NATURE 

3.  Eclipses. 

Giant  Sun  and  His  Family.     M.  Proctor.     Silver,  Burdett  &  Co. 

4.  Jupiter  and  its  moons. 

"Jupiter,  the  Solar  King."     Scientific  American  Supplement,  April  I, 
1916. 

5.  The  story  of  coal. 

Diggers  in  the  Earth.     E.  M.  Tappan.     Houghton  Mifflin  Co. 

6.  The  discovery  of  the  north  pole. 

Modern  Triumphs.     E.  M.  Tappan.     Houghton  Mifflin  Co. 

7.  The  story  of  oil. 

The  Story  of  Oil.     W.  S.  Tower.     D.  Appleton  &  Co. 

8.  Harnessing  Niagara  Falls. 

How  It  Is  Done.     A.  Williams.     Thos.  Nelson  &  Sons. 

9.  The  Elements  of  Descriptive  Astronomy.     H.  A.  Howe.     Silver,  Burdett 

&Co. 

BOOKS  THAT  WILL  HELP  YOU 

The  Field  and  Forest  Handy  Book.     D.  C.  Beard.     Chas.  Scribner's  Sons. 
Romance  of  Modern  Inventions.     A.  Williams.     J.  B.  Lippincott  Co. 
Scientific  American  Supplement. 

"Gasoline  from  Natural  Gas,"  March  18,  1916. 

"Notes  on  the  History  of  Coal  in  the  United  States,"  April  4,  1916. 

"The  Utilization  of  Peat,"  April  8,'  1916. 


UNIT  IV 
PROTECTION  —  HOMES  AND  CLOTHING 


PROJECT  XI 
BUILDING  OUR  HOMES 

Homes  in  different  parts  of  the  world.  Even  before  men 
emerge  from  a  savage  state  they  find  some  kind  of  a  home  neces- 
sary, to  protect  them  from  storms,  heat,  cold,  and  wild  animals. 
The  kind  of  home  which  people  have  depends  on  the  climate  and 
the  material  at  hand. 

An  Eskimo  builds  a  warm,  comfortable  home  out  of  blocks  of 
ice.  A  Bedouin  of  the  desert  builds  his  home  on  an  oasis  out  of 
mud  bricks  which  he  makes  from  clay  dug  from  under  the  sand. 
A  native  Hawaiian  builds  a  framework  of  bamboo  poles  and  covers 
it  with  grass.  The  Arab  in  his  woolen  tent,  the  Japanese  in  his 
light  house  of  bamboo  and  paper  screens,  the  mountaineer  in  his 
log  cabin,  all  utilize  for  their  homes  the  materials  which  they  can 
obtain  most  easily.  Those  of  us  who  live  in  the  country  may  live 
in  wooden  houses;  in  towns  we  live  in  houses  of  wood,  brick,  or 
cement;  in  cities  we  live  in  brick  blocks  or  in  great  apartment- 
houses  built  of  steel  and  concrete.  In  this  project  we  shall  find 
out  something  of  how  houses  are  built  and  of  the  materials  com- 
posing them. 

Your  home.  Each  of  you  lives  in  a  home.  You  may  spend  some 
time  learning  its  construction,  in  examining  its  convenience  and 
safety,  but  if  your  work  stops  there,  the  purpose  of  this  project 
will  not  be  attained.  Can  you  not  make  your  home  better,  safer, 
more  convenient?  Several  of  the  problems  and  individual  proj- 
ects will  give  you  suggestions  as  to  how  you  may  thus  improve 
your  home  conditions. 


226    PROTECTION  —  HOMES  AND  CLOTHING 

PROBLEM  i :  To  EXAMINE  MY  HOME  CONDITIONS. 

Directions: 

Find  the  answers  to  the  following  questions.     You  need  not  report  them 
to  the  class  unless  you  wish. 

A.  The  Location. 

1.  Is  the  house  located  on  high  or  low  land? 

2.  Are  the  surroundings  attractive? 

3.  Is  there  sufficient  space  around  the  house  to  afford  plenty  of 
light  and  air? 

4.  Are  the  neighbors  congenial? 

5.  Is  the  view  pleasant? 

6.  Is  the  street  quiet  or  noisy? 

7.  Are  any  offensive  odors  evident?     If  so,  may  their  source  be 
removed? 

8.  Is  the  house  conveniently  placed  for  school,  church,  and  busi- 
ness? 

B.  The  House  Surroundings. 

1.  Have  you  a  lawn  around  your  house?     If  so,  is  the  grass  neatly 
kept? 

2.  Do  flowers  and  shrubs  add  to  the  beauty  of  the  house  sur- 
roundings? 

3.  Have  you  space  for  a  vegetable  garden?      If  so,  is  it  so  well 
managed  that  it  helps  to  reduce  the  high  cost  of  living? 

4.  Are  the  trees  and  shrubs  well  placed?    Do  they  cause  any  unde- 
sirable effects,  such  as  dark  rooms,  dampness, .rotting  shingles, 
blocked  eave-spouts,  or  broken  cellar  walls? 

5.  Is  the  back  yard  as  attractive  as  the  front  yard? 

C.  Sunlight  and  Air. 

1.  In  what  direction  does  the  house  face? 

2.  Can  plenty  of  sunlight  and  air  enter  every  room?    To  test  this, 
make  a  list  of  the  rooms,  using  the  following  plan:  Name  of 
room.     Number  of  windows.     When  the  sun  shines  in. 

D.  Construction  and  Repair. 

1 .  Of  what  materials  is  the  house  built? 

2.  About  how  old  is  the  house? 

3.  Is  the  house  entirely  water-proof  and  wind-proof? 

4.  Are  there  any  signs  of  poor  repair,  such  as  torn  wall-paper, 
broken  plaster,  warped  or  broken  floors  or  woodwork?     If  so, 
can  you  do  anything  to  improve  these  conditions? 

E.  Drainage. 

1.  Is  the  house  located  on  high  land  or  on  low  land? 

2.  Is  the  soil  around  the  house  sandy  or  clayey? 


BUILDING  OUR  HOMES  227 

3.  Is  the  house  connected  with  a  sewer? 

4.  Is  all  the  plumbing  in  good  condition? 

5.  Is  the  cellar  ever  damp?     If  so,  when? 

F.  Water-Supply. 

1.  Is  your  water  supplied  by  the  city,  or  do  you  depend  on  a 
private  supply? 

2.  Do  you  know  whether  the  water  is  pure? 

3.  Do  you  know  what  its  source  is? 

4.  Do  you  know  how  the  water  is  brought  to  your  house? 

G.  Convenience. 

1.  Are  the  rooms  arranged  so  as  to  save  steps? 

2.  Does  each  person  have  a  separate  bedroom? 

3.  Does  each  room  have  an  independent  exit? 

4.  Are  there  enough  closets  in  the  house? 

5.  Are  the  stairs  safe  and  easy  for  old  people  and  little  children? 

H.  Sanitation. 

1.  Is  the  house  clean? 

2.  Are  there  any  dark  places  which  are  hard  to  clean,  making  good 
breeding  places  for  bacteria? 

3.  Are  the  floors  covered  with  carpets  or  with  removable  rugs? 

4.  Are  the  arrangements  for  storing  food  satisfactory? 

5.  Are  garbage,  ashes,  and  waste  allowed  to  accumulate? 

6.  Is  there  any  place  near  the  house  where  flies  or  mosquitoes  may 
breed? 

/.  Fire  Protection. 

1.  Is  the  house  built  of  fire-proof  material? 

2.  What  is  the  roof  covering? 

3.  Are  fire  exits  provided? 

4.  If  you  live  in  an  apartment  house  are  fire  escapes  provided? 

5.  Of  what  materials  are  the  fire  escapes  made?     Are  they  kept 
clear? 

6.  Are  there  fire  extinguishers  in  the  house?     Do  you  know  how 
to  use  one? 

7.  What  would  you  do  if  your  house  caught  fire? 

Summary: 

1.  Are  your  home  conditions,  in  general,  satisfactory  or  unsatis- 
factory? 

2.  Do  your  father  and  mother  agree  with  you  in  their  opinion 
about  your  home  environment? 

3.  What  can  you  do  to  improve  conditions? 


228    PROTECTION  —  HOMES  AND  CLOTHING 

PROBLEM  2 :  To  OBSERVE  A  HOUSE  WHILE  IT  is  BEING  BUILT. 
Directions: 

Visit  a  house  in  process  of  construction.     Find  out  all  you  can  about  the 
following  parts: 

1.  The  cellar. 

How  is  water  drawn  off? 

Is  the  floor  level  or  slightly  slanting?    Why? 

How  is  the  cellar  floor  made? 

Are  the  walls  "plumb"? 

Of  what  material  are  the  cellar  walls  made? 

Perhaps  you  find  a  layer  of  Portland  cement  on  the  outside.  What 
is  its  advantage? 

Perhaps  the  cellar  walls  are  double.  What  is  the  advantage  of 
such  an  arrangement? 

Perhaps  you  find  wire  mesh  buried  in  the  cement  around  the  cor- 
ners and  below  the  sills  of  the  house.  Why  is  it  used? 

2.  The  house  walls. 

Of  what  materials  are  the  walls  built? 
In  what  order  are  the  materials  put  together? 
What  are  the  advantages  of  air  spaces  in  the  walls? 
If  the  house  has  wooden  walls,  find  out 

a.  How  the  studs  or  uprights  are  held  firm. 

b.  How  far  apart  the  studs  are  placed. 

c.  What  covers  the  studding  on  the  outside. 

d.  What  covers  the  studding  on  the  inside. 

3.  The  roof. 

How  are  the  rafters  supported? 
How  far  apart  are  the  rafters? 
With  what  are  the  rafters  covered? 
Is  the  roof  covering  fireproof? 

4.  The  partitions. 

How  are  the  partitions  supported? 

With  what  are  the  studs  of  partitions  covered? 

How  are  the  openings  for  doors  and  windows  made? 

5.  The  floors. 

How  are  the  beams  or  joists  for  the  floors  supported? 
How  far  apart  are  the  beams? 
How  are  the  floor-boards  attached  to  the  beams? 
What  kind  of  wood  is  used  for  the  floor-boards? 
What  is  the  advantage  of  a  double  floor? 
How  are  the  ceilings  made? 

What  is  the  use  of  the  space  between  the  floor-boards  and  the  ceiling 
below? 
Summary: 

Prepare  an  oral  report  for  your  English  class  on  the  way  a  house  is  built. 


BUILDING  OUR  HOMES  229 

PROBLEM  3 :  To  STUDY  HOUSE  PLANS,  AND  TO  DETERMINE  THEIR  GOOD  AND 
BAD  POINTS. 

Directions: 

Bring  to  class  house  plans  taken  from  magazines. 

In  deciding  the  good  and  bad  points,  some  of  the  following  questions  may 
be  used  as  tests: 

1.  Are  the  entrances  convenient? 

2.  Do  the  windows  allow  sufficient  light? 

3.  Is  the  kitchen  well  planned,  of  convenient  size,  and  near  to  the 
dining-room? 

4.  Is  the  living-room  the  pleasantest  room  in  the  house? 

5.  Are  the  bath-rooms  conveniently  placed? 

6.  Are  there  plenty  of  closets? 

Question: 

Of  all  the  plans  examined,  which  would  you  prefer  for  your  own  house? 
State  reasons. 

PROBLEM  4:  ARE  THE  WALLS  OF  MY  HOUSE  "PLUMB"? 

Directions: 

Make  a  "plumb  line"  by  attaching  a  weight  to  a  cord. 

Try  holding  the  cord  in  different  positions.  'Where  does  the  weight 
point?  Why? 

Hold  your  plumb  line  near  the  walls  of  the  room,  near  the  tables,  and 
other  pieces  of  furniture,  near  the  outside  walls  of  the  house,  the  piazza 
rail,  etc. 

Can  you  find  anything  which  is  "out  of  plumb"?  If  so,  can  you  find 
any  causes? . 

Conclusion: 
Is  your  house  perfectly  plumb? 

PROBLEM  5 :  To  MAKE  A  CONCRETE  SLAB. 

Directions: 

Each  pupil  should  provide  himself  with  a  small  pasteboard  box.  Enough 
concrete  for  the  class  can  be  mixed  in  a  large  wooden  box  or  on  the  base- 
ment floor. 

To  make  concrete,  use  Portland  cement,  I  part;  sand,  2  parts;  and  peb- 
bles, 3  parts.  The  sand  must  be  sharp  and  clean.  Mix  the  cement  and 
the  sand  together  until  no  cement  can  be  seen.  Then  mix  the  pebbles  with 
it.  Into  a  hollow  in  the  center  of  the  mass  pour  water,  and  mix  rapidly 
until  the  whole  mass  is  of  a  pasty  consistency. 

Fill  your  small  box  with  a  layer  about  one  inch  thick,  and  set  it  away  to 
harden.  Watch  it  from  time  to  time.  When  the  concrete  is  hard,  pull 
off  the  pasteboard. 


230    PROTECTION  —  HOMES  AND  CLOTHING 

Question: 

In  what  respect  does  the  method  used  in  this  experiment  resemble  the 
method  used  in  making  a  concrete  building? 

PROBLEM  6:  To  MAKE  PLASTER. 

Directions: 

Mix  plaster  of  Paris  with  enough  water  to  make  a  thick  mud. 

Is  there  any  sign  of  chemical  action,  such  as  bubbles  or  heating? 

Pour  the  mud  into  a  mold  and  set  it  aside.  A  good  mold  is  a  tin  tray 
in  the  bottom  of  which  you  have  placed  an  attractive  picture,  face  down. 

Examine  the  mold  the  next  day.  What  is  the  condition  of  the  plaster? 
What  becomes  of  the  water? 

When  it  is  completely  set,  remove  it  from  the  mold. 

(Note:  pictures  of  famous  scientists  may  be  mounted  in  this  way  to 

hang  on  the  schoolroom  wall.) 

Question: 

Why  do  barrels  which  contain  lime  sometimes  burst? 

PROBLEM  7:  WHAT  ROOFING  MATERIALS  ARE  FIREPROOF? 

Directions: 

Procure  samples  of  various  materials  used  for  roofing  such  as  shingles, 
asbestos  roofing,  asphalt  shingles,  tar  paper,  etc. 

Try  to  set  fire  to  the  materials  with  a  match.  Try  holding  them  in  a 
Bunsen  flame. 

Summary: . 

Show  your  results  in  a  table: 


MATERIAL 

EFFECT  OF  MATCH 

EFFECT  OF  BUNSEN  FLAME 

Question: 

Which  is  the  most  fireproof  roofing  material  you  tested? 

PROBLEM  8 :  WHERE  DOES  GROWTH  TAKE  PLACE  IN  A  TREE? 

Directions: 

Procure  the  end  of  a  small  branch  from  a  tree.     Maple,  oak,  horse- 
chestnut,  or  ash  are  good. 


BUILDING  OUR  HOMES 


231 


Find  out  how  much  of  the  branch  grew  last  season  by  examining  the 
bark,  starting  at  the  tip  and  tracing  the  growth  back  to  a  small  ring  around 
the  twig,  the  ring  of  growth. 

Cut  across  the  twig  of  last  season,  and  examine  the  cut  surface  with  a 
magnifying  glass.  What  is  the  difference  in  color  between  the  bark  and 
the  wood? 

Can  you  find  any  other  rings  of  growth  on  the  twig? 

Can  you  find  out  how  old  the  twig  is? 

How  many  years  has  this  little  twig  been  growing?  How  many  rings  of 
wood  can  you  see  in  its  oldest  part?  How  does  the  number  of  rings  com- 
pare with  the  number  of  years  of  growth? 

Conclusion: 
Where  do  new  twigs  grow? 

Questions: 

1.  Do  all  trees  grow  the  same  amount  in  a  season? 

2.  A  tree  which  was  cut  down  was  found  to  contain  149  rings  of  wood. 
How  long  had  it  been  growing? 

PROBLEM  9:  How  is  WOOD  MADE?  ar: 

Directions: 

Examine  a  cross-section  of  wood  at 
least  an  inch  in  diameter. 

Make  a  careful  drawing  of  the 
cross-section,  labeling  carefully  all 
the  following  parts  which  you  can 
distinguish: 

Annual  rings  of  wood. 

Ducts  for  carrying  water. 

Green  layer  of  bark. 

Corky  layer  of  bark. 

Epidermis  or  skin  or  the  bark. 

(Note:  Two  layers  you  probably 
cannot  see.  Between  the  wood 
and  the  bark  is  a  layer  of  rapidly 
growing  cells  called  the  cambium 
or  growing  layer.  This  layer  forms 
wood  cells  from  the  inner  surface, 
and  bark  from  its  outer  surface. 
The  ring  of  new  wood  is  thus  formed 
outside  the  old  wood. 

The  inner  layer  of  bark  consists  of  tube-like  cells  which  carry  the  food 
from  the  leaves  towards  the  roots.     It  is  called  the  bast  layer.) 


FIG.  113.  The  structure  of  hardwood, 
showing  the  appearance  of  the  cross-section 
and  the  lengthwise  or  radial  section.  B,  bark; 
S,  sapwood;  H,  heartwood;  ar,  annual  rings; 
mr,  medullary  rays. 


232     PROTECTION  —  HOMES  AND  CLOTHING 

Conclusions: 

1.  How  many  growing  seasons  are  needed  to  form  a  ring  of  wood? 

2.  Where  is  the  new  wood  formed? 

3.  Does  the  bark  increase  in  thickness  as  fast  as  the  wood? 

PROBLEM  10:  How  is  WOOD  CUT? 

Directions: 

Examine  pieces  of  wood  showing  the  three  methods  of  cutting  —  cross- 
section,  radial  section,  and  tangential  section. 
In  each  section  locate  — 
Annual  rings. 
Ducts  or  "water-pipes." 
Closely  packed  wood  cells. 

(In  some  wood,  such  as  oak,  you  may  see  medullary  rays,  consisting 
of  narrow  radiating  lines  of  tightly  packed  cells.) 

Can  you  see  any  difference  between  the  heartwood  and  the  sapwood? 
Which  is  older? 

Can  you  find  out  what  causes  a  knot  in  the  wood? 
Examine  your  desk,  the  teacher's  desk,  the  floor,  the  door,  and  any  other 
wood  at  hand  and  decide  how  it  was  cut. 

Conclusions: 

1.  How  is  most  wood  cut? 

2.  Which  method  of  cutting  produces  the  most  attractive  grain? 

PROBLEM  1 1 :  To  COMPARE  HARDWOODS  AND  SOFTWOODS. 

Directions: 

Part  i.  Collect  leafy  twigs  from  as  many  trees  as  possible,  including  the 
evergreen  trees. 

Arrange  two  collections.  In  one,  place  all  the  twigs  with  needle-shaped 
or  small  scale-like  leaves.  These  are  all  from  softwood  trees.  In  the  other 
collection  place  all  the  twigs,  the  leaves  of  which  are  not  needle-shaped  or 
scale-like.  These  are  the  broad-leaved  or  hardwood  trees. 

Optional: 

Determine  from  the  teacher  or  from  a  key  the  kind  of  tree  from  which 
each  twig  was  taken.  List  in  a  table  in  your  notebook  the  trees  which  you 
determine. 


SOFTWOOD  TREES 

HARDWOOD  TREES 

BUILDING  OUR  HOMES 


233 


Part  2.  Examine  the  cut  ends  of  the  softwood  twigs. 

Can  you  see  the  annual  rings? 

Can  you  see  any  ducts  or  pores? 

Examine  the  cut  ends  of  the  hardwood  twigs. 

Are  the  ducts  present? 

Summary: 

1.  What  are  the  differences  in  the  leaves  of  softwood  and  hardwood 
trees? 

2.  What  are  the  differences  in  the  structure  of  the  wood? 

PROBLEM  12:  To  DETERMINE  THE  USES  OF  DIFFERENT  KINDS  OF  WOOD  IN 

OUR  HOUSES. 
Directions: 

From  consultation  with  carpenters  and  a  study  of  reference  books  find 
out  the  uses  of  as  many  kinds  of  wood  as  possible.  Record  your  results  in 
a  table: 


WOODS  USED  FOR 

House  timbers 

Shingles 

Clapboards 

Walls 

Doors 

Woodwork 

Furniture 

Floors 

Indicate  which  are  hardwoods  and  which  are  softwoods. 

Question: 

If  the  wood  is  to  be  covered  by  paint,  plaster,  etc.,  is  a  hardwood  or  a 
softwood  more  commonly  used? 

PROBLEM  13:  WHY  DO  BRICKS  CRUMBLE? 

Directions: 

Procure  several  bricks  of  different  kinds.     Be  sure  that  they  are  dry. 
Weigh  each  brick. 


234     PROTECTION  —  HOMES  AND  CLOTHING 

Place  them  in  a  large  kettle  of  water.  What  passes  from  the  brick  into 
the  water?  Why? 

Heat  the  water.     Explain  any  changes  that  you  see. 

Finally  boil  the  water  ten  minutes.    Let  it  cool  to  room  temperature. 

Weigh  each  brick  again. 

Calculate  the  percentage  of  water  absorption  in  each  brick. 

Conclusion: 
How  do  bricks  absorb  water? 

Question: 

If  the  water  should  freeze  in  the  pores  of  the  brick  what  result  would 
you  expect? 

PROBLEM  14 :  To  COMPARE  BUILDING  STONES. 

Directions: 

Procure  pieces  of  granite,  sandstone,  limestone,  and  marble. 

On  each  stone  drop  a  little  acid.  Which  show  signs  of  a  chemical  action? 
Which  would  you  expect  to  wear  away  most  easily  as  a  result  of  the  action 
of  the  weather? 

Hit  each  stone  with  a  hammer.     Which  seems  the  hardest? 

Scratch  each  stone  with  a  knife  blade.  Which  would  wear  away  most 
quickly  where  there  is  friction? 

Weigh  each  stone  dry.  Soak  them  in  water  some  time,  and  weigh  again. 
Which  has  absorbed  the  largest  percentage  of  water?  Which  is  most 
porous?  Which  would  allow  water  to  freeze  in  its  pores  and  cause  crum- 
bling? 

Find  out  the  cost  of  each  kind  of  stone. 
Summary: 

Sum  up  the  advantages  and  disadvantages  that  you  have  found  for  each 
stone,  as  a  building  material. 

Choosing  a  house.  Some  day  you  may  build  a  house.  It  is  not 
too  soon  to  decide  some  of  the  good  points  which  you  may  wish 
to  have  in  your  house.  Perhaps  your  family  is  to  move  before 
long.  What  points  are  you  going  to  consider  in  choosing  your 
new  home?  A  home  need  not  be  costly  to  be  convenient  and 
home-like.  Indeed  some  of  the  costliest  homes  are  the  least 
attractive. 

A  convenient  house.  In  choosing  a  home  think  first  of  con- 
venience. A  house  is  the  home-maker's  workshop.  The  more 
easily  her  work  is  done,  the  more  likely  she  is  to  be,  not  a  mere 
house-keeper,  but  a  true  home-maker.  If  your  father  and  mother 


BUILDING  OUR  HOMES 


235 


allow  you  to  help  choose  a  new  home,  think  not  only  of  the  attrac- 
tive outside  appearance,  but  of  the  convenience,  especially  for 
your  mother. 

First,  examine  the  kitchen.   The  kitchen  is  the  heart  of  a  home. 
If  the  food  for  the  family  is  to  be  pure  and  clean,  the  place  where 


FIG.  114.  A  kitchen  to  be  proud  of. 

it  is  prepared  must  be  light  and  clean.  It  need  not  be  large,  but 
it  must  have  a  good  circulation  of  air.  The  fewer  steps  that  are 
necessary  between  pantry  or  working  cabinet,  stove  and  sink, 
the  more  convenient  the  kitchen  is. 

The  bedrooms  should  have  a  good  supply  of  fresh  air  and  sun* 
light  if  possible.  Sunlight  is  the  greatest  enemy  of  bacteria. 
Wall-space  to  allow  a  convenient  arrangement  of  furniture,  a  light, 
cheerful  wall-paper  with  few  pictures  or  ornaments,  and  a  good 
closet,  ought  to  be  looked  for  in  a  bedroom. 

The  living-room  is  the  place  in  the  house  where  we  really  live. 
It  should  be  the  most  attractive  room  in  the  house.  Plenty  of 
light,  plenty  of  fresh  air,  plenty  of  warmth  in  the  winter,  plenty 


236    PROTECTION  —  HOMES  AND  CLOTHING 

of  comfortable  places  to  sit,  plenty  of  room  for  books  and  work, 
—  these  are  what  it  needs.  Wall-space  well  arranged  for  furniture, 
floors  easy  to  clean,  not  too  many  small  articles  to  dust  —  these 
are  points  to  be  considered  in  looking  for  convenience  for  the 
home-maker. 

Stairs  should  be  wide  enough  to  allow  furniture  to  be  carried 
and  not  too  steep  for  comfort.  The  bathroom  should  be  easily 
accessible  to  all,  and,  above  everything  else,  well  ventilated.  A 
servant's  room  should  be  airy,  light,  and  attractive. 

The  problems  of  a  city-dweller  in  choosing  a  house  are,  of 
course,  somewhat  different  from  those  of  a  country-dweller.  In 
an  apartment  house  notice  the  arrangement  of  the  air-shaft.  See 
that  windows  are  not  directly  opposite  the  windows  of  the  next 
apartment.  See  if  fire  escapes  are  well  placed  and  easy  of  access. 

A  safe  house.  What  are  the  dangers  in  a  house?  First  and 
most  important  is  fire.  The  hazards  of  the  house  have  increased 
in  modern  times,  because  of  the  use  of  gas  and  electricity  as  well 
as  of  matches,  gasoline,  kerosene,  and  the  like. 

The  dangers  from  electricity  are  of  two  kinds,  shock  and  fire. 
An  electric  current  may  be  likened  to  the  flow  of  water  in  a  hose. 
The  force  which  causes  the  water  to  flow  is  the  water  pressure  in 
the  reservoir,  while  that  which  causes  the  electric  current  to  flow 
is  the  voltage,  or  electrical  pressure,  on  the  wires  entering  the 
house.  A  leak  in  a  hose  allows  water  to  escape.  A  faulty  insula- 
tion, or  protection,  of  the  electric  wire,  may  allow  the  current  to 
escape  and  cause  serious  injury,  even  death.  Shocks  and  burns 
are  caused  when  a  current  passes  through  the  body.  Avoid 
touching,  at  the  same  time,  an  electric  light  and  any  other  me- 
tallic object,  such  as  a  plumbing  fixture,  a  radiator,  or  a  tele- 
phone. 

Fires  may  be  caused  by  defective  insulation.  If  the  wire  is  un- 
protected a  spark  may  pass  between  the  wire  and  some  nearby 
material.  Fires  may  also  be  caused  by  the  overheating  of  elec- 
tric devices  like  irons,  toasters,  etc.  To  prevent  the  passage 
of  too  large  currents  and  the  consequent  overheating,  fuses  are 
used.  A  fuse  is  a  part  of  the  circuit  which  melts  if  the  current  is 
too  great. 


BUILDING  OUR  HOMES  237 

The  dangers  from  gas  are  four:  asphyxiation,  burns,  destruction 
by  fire,  and  explosions.  Asphyxiation  means  smothering.  Smoth- 
ering results  from  depriving  the  cells  of  the  body  of  their  neces- 
sary oxygen.  Illuminating  gas  contains  one  very  dangerous 
substance,  called  carbon  monoxide.  When  it  enters  the  lungs  it 
immediately  finds  its  way  to  the  little  red  corpuscles,  which 
usually  carry  the  oxygen.  When  loaded  with  this  dangerous 
gas,  they  cannot  carry  oxygen,  and  the  cells  are  therefore  unable 
to  perform  their  work.  A  person  soon  becomes  unconscious 
and  finally  dies  unless  fresh  air  or  oxygen  can  be  given  him. 
Artificial  respiration  is  often  necessary.  (See  page  47.)  Gas 
which  burns  incompletely,  as  when  it  "  flashes  back,"  may  pro- 
duce the  deadly  carbon  monoxide.  "  Coal  gas  "  from  kitchen 
ranges  and  furnaces  may  also  contain  it. 

Fires  may  result,  not  only  from  the  direct  flame,  but  also  from 
an  overheated  condition  of  nearby  articles,  such  as  wood,  lath, 
and  plaster. 

Unless  gas  is  mixed  with  air,  it  cannot  explode.  If  it  is  mixed 
in  a  certain  proportion,  and  a  flame  or  electric  spark  is  near,  a 
dangerous  explosion  may  result. 

In  choosing  a  new  home  make  sure  that  the  wiring  is  safe,  and 
that  gas  fixtures  do  not  leak.  Anyway  be  sure  that  matches, 
kerosene,  and  gasoline  are  kept  in  safe  places.  Examine  your 
own  home  to  find  whether  you  can  reduce  in  any  way  the  danger 
from  fire. 

How  a  house  is  built  —  the  foundations.  A  house  begins  with 
its  foundations.  Never  lease  a  house  without  looking  at  the  cellar. 
Two  requirements  for  a  cellar  are :  it  must  be  dry,  and  the  foun- 
dation must  be  strong.  Dampness  in  the  cellar  causes  mold  to 
grow  on  food  kept  there,  and  worse  still,  may  cause  disease. 
Even  if  you  are  selecting  an  apartment,  look  at  the  cellar  before 
deciding  on  it.  One  family  who  lived  in  an  apartment  had 
illness  after  illness  all  winter ;  in  the  spring  they  found  that  a  foot 
of  water  had  stood  in  the  cellar  for  months.  This  may  have 
caused  the  illness. 

The  cellar  floor  should  not  be  perfectly  level,  but  should  slant 
to  allow  water  to  run  off  through  a  drain.  The  floor  should 


238     PROTECTION --HOMES  AND  CLOTHING 

be  made  of  a  mixture  of  sand,  broken  stone,  and  cement,  with 
Portland  cement  laid  over  it  and  made  smooth.  Portland  ce- 
ment and  sand  are  the  best  materials  for  a  cellar.  Portland 
cement  is  found  in  a  natural  state  in  many  places.  It  may  be 
made  by  heating  together  limestone,  clay,  and  sand  in  the  right 
proportions,  and  grinding  the  "  clinker  "  thus  formed  to  a  dust. 
When  it  is  mixed  with  water  a  chemical  action  takes  place  which 
makes  a  hard  rock-like  mass,  even  under  water.  An  old  cellar 
may  be  made  waterproof  by  adding  such  a  coating. 

In  order  to  be  strong  enough  to  support  the  rest  of  the  house 
and  to  prevent  settling  and  cracking  of  walls,  the  cellar  walls  must 
remain  plumb.  A  plumb  line  is  a  cord  with  a  weight  hanging  from 
it.  The  attraction  of  the  earth  pulls  the  weight  downwards. 
(See  page  223.)  A  plumb  line  points  directly  toward  the  center 
of  the  earth.  The  stability  of  the  foundation  can  be  insured  by 
making  a  footing  of  stone  or  cement  at  the  time  of  building. 

The  house  walls.  A  house  must  give  protection  from  the  cold 
of  winter  and  from  the  greatest  heat  of  summer.  The  walls  must 
not  readily  conduct  the  heat  out  of  the  house  in  winter,  nor  into 
the  house  in  summer.  One  of  the  best  non-conductors  of  heat  is 
air  at  rest.  Walls  are  therefore  made  double,  with  a  space  for 
air.  The  inner  walls  are  usually  covered  with  plaster.  Do  you 
know  why  double  windows  are  sometimes  used  in  winter? 

Plaster  is  useful  in  furnishing  a  smooth  surface  on  which  to  place 
wall  paper,  and  to  absorb  sound.  It  may  be  fastened  to  wood 
laths,  metal  laths,  concrete,  tile,  brick,  or  plaster  board.  Usu- 
ally there  are  three  coats:  a  scratch  coat,  a  brown  coat,  and  &  finish 
coat.  The  latter  is  what  we  see  on  a  finished  wall.  It  is  made  of 
lime  and  plaster  of  Paris,  made  into  a  paste  with  water.  The 
plaster  of  Paris  combines  with  the  water  and  forms  a  hard  coating. 

The  floors.  Wood  is  the  usual  material  for  floors.  Hard- 
wood floors  are  beautiful  and  healthful  because  they  allow  rugs 
to  be  used  and  can  be  easily  cleaned.  Softwood  floors  may  be 
painted  or  covered  with  linoleum.  For  the  kitchen,  linoleum  is 
especially  satisfactory.  The  wood  for  floors  should  be  well  sea- 
soned to  prevent  warping  and  should  be  double,  so  that  the  floor 
may  act  as  a  heat  and  sound  absorber. 


BUILDING  OUR  HOMES  239 

The  roof.  One  of  the  most  important  parts  of  the  house  is  its 
roof.  It  should  be  waterproof,  fireproof,  durable,  and  a  poor 
conductor  of  heat. 

Shingles  are  commonly  used  on  slanting  roofs.  Cedar  shingles 
are  desirable  because  they  do  not  decay  quickly.  Shingles  are 
sometimes  treated  with  liquid  asphalt  to  make  them  more  dura- 
ble and  fireproof. 

Felt,  saturated  with  tar  or  with  asphalt,  is  used  on  many  houses, 
and  is  usually  covered  with  a  layer  of  pitch  or  asphalt  and  a  layer 
of  gravel. 

Tiling  is  a  beautiful  roofing  for  concrete  or  stucco  houses,  but 
it  is  expensive  and  very  heavy. 

Materials  used  in  building  our  houses.  An  interesting  prob- 
lem will  be  for  you  to  find  out  what  percentage  of  the  class  live 
in  wooden  houses,  what  percentage  in  brick  houses,  and  what 
percentage  in  houses  built  of  other  materials.  Compare  your 
class  with  a  class  of  children  in  London,  or  in  Rio  de  Janeiro,  in 
Christiania,  or  in  a  village  in  Russia.  Try  to  find  out  how  homes 
in  those  places  are  made,  and  explain  how  the  climate  and  the  ma- 
terials which  are  available  account  for  their  differences. 

Wood  as  a  building  material.  Wood  is  different  from  all  other 
building  materials  because  it  has  once  been  alive.  It  is  an  organic 
substance,  composed  of  cells.  (See  page  152.)  Many  of  the  ad- 
vantages of  wood  are  due  to  the  cells.  They  are  tiny,  hollow 
tubes,  usually  closed  at  the  end.  They  last  for  years  after  the 
protoplasm  which  made  them  is  dead.  The  empty  cells  act  as 
air  spaces  and  prevent  the  passage  of  heat  and  sound.  Because 
wood  is  porous,  preservatives  can  be  forced  into  the  cells,  and 
paint  will  cling  to  its  surface. 

The  grain  of  wood.  Wood  is  beautiful  because  of  its  grain.  Perhaps, 
even  though  you  have  tried  the  problems  on  page  232,  you  do  not  fully 
understand  what  causes  the  grain.  Trees  that  grow  in  temperate  climates 
grow  faster  in  the  spring  of  the  year  than  in  the  summer.  The  cells  in  the 
spring  wood  are  usually  larger  than  those  in  the  summer  wood.  No  growth 
at  all  takes  place  in  the  winter.  We  can  see,  therefore,  a  distinct  annual 
ring  for  each  year's  growth. 

If  the  tree  is  cut  across  the  grain  we  can  see  each  year's  growth  as  a  real 
ring.  The  oldest  wood  is  in  the  center  of  the  tree,  in  the  heartwood.  The 


240     PROTECTION  — HOMES  AND  CLOTHING 


newest  ring  is  next  to  the  bark  in  the  sapwood,  for  the  layer  between  the 
bark  and  the  wood  is  the  growing  layer  of  the  tree. 

If  the  lumber  is  sawed  into  boards,  it  may  be  sawed  parallel  to  the  fibers, 
as  shown  in  the  diagram  of  a  radial  section.  (See  figure  113.)  It  may  also  be 
sawed  to  cross  the  wood-fibers  at  a  slight  slant,  thus  causing  the  appearance 
of  the  tangential  section.  The  latter  way  of  sawing  produces  the  most  beau- 
tiful grain.  The  figure  in  bird's-eye  maple  is  caused  by  slight  irregularities 
in  the  annual  rings. 

Hardwoods  and  softwoods.  The  woods  commonly  used  are  di- 
vided into  two  large  classes :  the  hardwoods,  or  woods  from  broad- 
leaved  trees;  and  the  softwoods,  which  are  woods  from  trees  with 

needle-like  or  scale-like  leaves.  The 
latter  have  their  seeds  in  cones,  and 
are  therefore  sometimes  called  conifers 
(cone-bearers).  In  climates  where  the 
winter  is  severe,  the  hardwoods  all  drop 
their  leaves  in  the  winter,  while  the  soft- 
woods are  evergreen,  with  the  exception 
of  the  tamarack. 

It  is  unfortunate  that  the  terms 
hardwood  and  softwood  are  used,  be- 
cause some  so-called  softwoods,  as  yel- 
low pine  and  tamarack,  are  consider- 
ably harder  than  many  hardwoods; 
and  some  so-called  hardwoods,  as  cot- 
tonwood  and  basswood,  are  almost  as 
soft  as  any  softwood.  The  real  differ- 
ence is  a  difference  in  cell-structure. 

All  hardwoods  have  ducts  or  water  pipes,  which  are  cells  with 
open  ends  that  form  tubes  extending  all  the  way  up  the  tree- 
trunk.  These  cells  are  much  larger  than  the  cells  of  the  wood 
fibers,  and  show  plainly  in  the  grain  of  some  wood,  as  oak,  chest- 
nut, and  walnut. 

Softwoods  have  no  ducts  for  carrying  water.  Water  passes  by 
osmosis  (see  page  156)  through  the  walls  of  the  long,  narrow, 
pointed  cells,  and  so  reaches  the  leaves.  Some  softwoods  have 
tubes  to  carry  resin,  or  pitch,  which  causes  them  to  burn  with  a 
bright  flame. 


FIG.  115.  Softwood.  A  view  of 
sugar  pine  as  seen  through  a  micro- 
scope. Find  portions  of  two  annual 
rings,  with  large  cells  or  tracheids 
in  the  spring  wood  and  smaller  cells 
in  the  summer  wood.  Two  special 
tubes  for  carrying  resin  (RD)  are 
shown.  Softwood  has  no  ducts  for 
carrying  water. 


BUILDING  OUR  HOMES 


241 


Why  wood  differs  in  value  for  building  purposes.  All  wood  is  not 
equally  valuable.  In  house-building  one  thing  to  consider  is  the  amount 
of  moisture  in  the  wood.  Green  lumber  may  contain  water  equal  to  two 
thirds  its  total  weight.  Wood  is  seasoned  to  allow  the  water  to  evapo- 
rate. Lumber  may  be  dried  by  stacking  it  so  as  to  expose  it  to  the  air 
for  a  year  or  more,  or  it  may  be  placed  in  a  dry  kiln  for  several  weeks. 
Wood  to  be  used  inside  of  houses  should  contain  from  five  to  eight  per 
cent  of  moisture.  If  the  wood  is  drier  it  will  swell  by  absorbing  moisture 
from  the  atmosphere,  thereby  causing  floors  to  bulge  and  doors  to  stick; 
and  if  it  contains  more  moisture  it  will  dry  out  and  crack  as  soon  as  the 
rooms  are  heated.  Wood  to  be  used  for  interior  finish  should  therefore 
always  be  kiln-dried  because  the  amount  of  water  can  in  that  way  be 
controlled. 

Another  factor  which  influences  the  value  of  wood  is  its  weight.  Usually 
heavy  woods  are  stronger  and  harder  than  light  woods.  Very  light  or  very 
heavy  wood  should  not  be  chosen  for  furniture. 

The  conductivity  of  wood  is  important.  It  conducts  or  carries  heat 
much  more  slowly  than  metals  or  stone  because,  of  the  air  in  the  cells. 
Therefore  it  is  used  for  handles  on  dishes  and  pans,  for  refrigerator  walls,  for 
fireless  cookers,  and  for  the  floors  and  walls  of  the  house  itself.  It  is  inter- 
esting to  know  that  wood  conducts  heat  twice  as  fast  with  the  grain  as 
across  it.  Sound  is  conducted  along  the  fiber  fairly  well,  but  only  about  a 
third  as  fast  across  the  grain. 

The  presence  of  knots  detracts  from  the  value  of  wood.  A  knot  is  caused 
by  a  branch  leaving  the  stem. 

The  cost  of  wood  depends  partly  upon  the  ease  with  which  it  is  obtained 
from  the  forests  and  the  distance  to  market. 

The  durability  of  wood  depends  upon  its  resistance  to  the  bacteria  of 
decay.  Wood  does  not  decay  if  perfectly  dry,  because  bacteria  need  mois- 
ture for  growth.  Strangely  enough,  neither  does  wood  decay  if  under 
water.  Wood  taken  from  the  bottom  of  an  old  well  has  been  found  per- 
fectly sound,  although  it  may  have  lain  there  hundreds  of  years.  The 
reason  is  that  when  the  wood  becomes ' '  water-logged  "  the  cells  are  filled  with 
water  instead  of  air.  The  bacteria  of  decay  need  air  to  help  them,  so  the 
wood  is  preserved.  The  heartwood  is  more  durable  than  sapwood.  From 
a  study  of  the  table  what  woods  would  you  advise  for  posts?  for  shingles? 

Relative  durability  of  common  woods. 

CONIFERS 


Very  durable 

Durable 

Intermediate 

Non-durable 

Cedar 
Cypress 
Redwood 

Fir 
Tamarack 
Pine,  longleaf 
Pine,  eastern  white 

Hemlock 
Other  pines 

Spruce 

242     PROTECTION  —  HOMES  AND  CLOTHING 


HARDWOODS 


Very  durable 

Durable 

Intermediate 

Non-durable 

Chestnut 

Cherry 

Ash 

Basswood 

Black  walnut 

White  oaks 

Butternut 

Beech 

Black  locust 

Red  gum 

Birch 

Poplar 

Buckeye 

Red  oaks 

Cottonwood 

White  elm 

Maples 

Sycamore 

Cotton  gum 

A  brick  house.  Street  after  street  in  some  cities  is  lined  with 
a  double  row  of  brick  houses,  nearly  alike.  Brick  is  a  very  com- 
mon material  for  a  house.  Yet  some  of  the  most  beautiful  coun- 
try houses  of  wealthy  people  are  built  of  brick. 

Bricks  are  made  of  clay  or  of  powdered  shale.  (See  page  127.) 
Three  ways  of  making  them  are  in  common  use.  The  first  and 
simplest  way  is  to  press  the  soft  wet  clay  into  wooden  molds  by 
hand  or  by  machine  and  then  to  dry  them  in  a  kiln.  Houses 
built  of  these  soft-clay  bricks  were  used  in  the  middle  ages.  The 
colonial  houses  of  Virginia  were  built  of  them. 

A  second  kind  of  brick  is  the  dry -pressed  brick.  This  is  made  by 
grinding  the  clay  into  a  moist  powder  and  shaping  it  by  powerful 
presses,  then  drying  and  firing.  The  bricks  so  made  are  perfectly 
shaped  and  very  compact.  They  are  either  red  or  yellow,  accord- 
ing to  the  kind  of  clay  used.  They  are  too  smooth  and  regular  to 
be  attractive  for  use  in  the  most  expensive  houses,  but  are  widely 
used  for  schools,  office  buildings,  and  apartment  houses. 

The  most  beautiful  bricks  are  made  by  the  stiff-clay  process. 
Stiff  clay  is  forced  through  a  machine  much  like  a  large  meat 
grinder.  Out  of  it  comes  a  band  of  clay  the  width  and  thickness 
of  a  brick.  By  wires  stretched  between  the  two  sides  of  a  frame 
the  long  band  is  cut  into  lengths  to  make  bricks.  Then  they  are 
dried  and  fired,  as  every  brick  must  be.  Variation  in  color  from 
bronze  to  red  and  almost  to  black,  or  from  buff  to  golden  brown, 
adds  to  the  beauty  of  these  bricks. 

The  saying,  "  Bricks  without  straw,"  refers  to  the  bricks  made 


BUILDING  OUR  HOMES 


243 


by  the  ancient  Hebrews  in  the  land  of  Egypt,  thousands  of  years 
ago.  Then  straw  was  used  to  hold  the  clay  together.  Nowa- 
days all  bricks  are  bricks  without  straw. 

Bricks  are  apt  to  crack  and  crumble  after  a  severe  winter.  The 
little  spaces  between  the  particles  of  clay  are  usually  filled  with 
air.  Water  may  penetrate  the  brick  in  winter  storms,  and  freeze 
to  ice  within  the  bricks.  The  expansion  to  ice  breaks  the  brick 
and  the  outside  layer  scales  off. 

Brick  houses  are  warm  in  winter  and  cool  in  summer  because 
the  bricks  are  porous.  The  air  in  the  pores  is  a  better  non- 
conductor of  heat  than  the  clay.  Bricks  are  practically  fireproof 
in  themselves,  but  when 
built  around  a  wooden 
frame  they  will  fall  off 
and  allow  the  house  to  col- 
lapse as  the  wood  burns. 

Concrete  construction. 
Portland  cement  is  used, 
mixed  with  gravel ,  crushed 
stone,  and  water,  to  make 
concrete.  The  mass  be- 
comes as  hard  as  a  stone. 
It  is  easy  to  handle  as  a 
building  material.  Wet 
concrete  is  poured  into  a 
rough  mold  made  of 
boards,  which  are  removed 
as  soon  as  the  concrete  has 
' '  set "  and  used  over  again . 
Reinforced  concrete  is  made 


FIG.  116.  A  building  of  structural  steel. 
(Courtesy,  American  Bridge  Co.) 


by  embedding  metal  rods 
or  wire  mesh  in  the  concrete.  It  is  used  very  widely  in  construct- 
ing great  office  buildings  and  apartment  houses.  Many  convenient 
devices  about  a  home  and  farm  may  be  easily  made  of  concrete. 
A  mixture  which  is  too  u  rich  "  has  so  much  cement  that  it 
cracks.  A  "  lean  "  mixture  with  a  larger  proportion  of  sand  is  more 
porous  and  does  not  crack  so  readily. 


244 


PROTECTION  —  HOMES  AND  CLOTHING 


A  house  of  stucco.  A  popular  modern  finish  for  houses  is 
stucco,  which  is  a  plaster  applied  to  the  outside  of  a  house.  It  is 
usually  laid  on  a  wooden  frame  and  held  in  place  by  wood  or 
metal  laths.  The  surface  is  usually  left  rough,  since  a  rough  sur- 
face is  less  liable  to  show  cracks.  The  advantages  of  stucco  are 
that  it  gives  warmth,  is  attractive  in  appearance,  and  saves  money, 
since  no  painting  is  necessary. 

Building  stones.  In  your  study  of  rocks  you  have  learned  that 
there  are  three  great  divisions.  (See  page  125.)  Each  of  these 
divisions  furnishes  one  or  more  common  building  stones. 


FIG.  117.  A  marble  quarry  in  Vermont.    The  great  slabs  are  cut  by  means  of 
steam  drills  and  moved  by  derricks.     (Copyright,  Keystone  View  Co.) 

Granite,  formed  by  the  action  of  heat,  is  a  very  hard  rock.  It 
is  so  compact  that  water  cannot  enter  it  easily,  so  it  does  not 
crumble  by  the  action  of  frost.  None  of  the  materials  composing 
it  dissolves  easily  in  water,  so  the  rain  does  not  weather  it  quickly. 
Neither  does  it  break  because  of  the  changes  of  temperature  be- 


BUILDING  OUR  HOMES  •  245 

tween  hot  days  and  cold  nights.  No  load  is  heavy  enough  to 
cause  it  to  bend.  Granite  is  therefore  a  most  durable  building 
stone,  but  it  is  too  expensive  for  common  use. 

Two  sedimentary  rocks  are  used  for  buildings.  Sandstone  con- 
sists of  grains  of  sand  cemented  together.  If  iron  is  present  in 
the  cement,  the  sandstone  is  red.  Most  sandstones  are  porous 
and  soft.  They  are  apt,  therefore,  to  crumble  from  the  action  of 
heat  and  cold,  and  from  water  getting  into  the  pores  and  freez- 
ing. Sandstone  is  so  porous  that  the  particles  are  easily  moved 
in  it,  so  it  bends  out  of  shape  if  a  heavy  load  is  placed  upon  it. 
It  is  often  used  for  trimming  brick  houses. 

Limestone  is  another  sedimentary  rock  used  for  buildings.  It 
is  made  of  tiny  shells  and  skeletons.  (See  page  127.)  Since  lime- 
stone is  acted  on  chemically  by 'water  which  contains  carbon 
dioxide,  the  face  of  the  stone,  in  contact  with  the  air,  is  apt  to 
weather  badly.  Limestone  is  compact  and  strong  enough  to  bear 
any  load  without  bending. 

The  metamorphic  rock  used  for  building  is  marble,  the  most 
beautiful  of  all.  Its  composition  is  like  that  of  limestone  and  it 
behaves  much  the  same  when  exposed  to  the  weather.  It  is  soft 
enough  to  be  worn  rather  quickly,  as  may  be  seen  in  the  case  of 
marble  steps.  Yet  it  is  so  attractive  in  its  gleaming  whiteness 
that  for  the  costliest  of  buildings,  as  for  our  National  Capitol,  we 
use  this  queen  of  building  stones. 

INDIVIDUAL  PROJECTS 

Working  projects: 

1 .  Clean  the  schoolyard. 

2.  Clean  the  yard  at  home. 

3.  Whitewash  a  cellar. 

Find  out  from  a  mason  or  from  your  father  how  to  mix  the  whitewash. 

4.  Make  a  useful  article  of  concrete. 

Send  for  directions  concerning  the  use  of  concrete. 

5.  Make  a  leaking  cellar  waterproof. 

Find  out  from  a  mason  how  to  mix  the  Portland  cement  and  how  to 
apply  it. 

6.  Make  a  collection  of  pictures  of  historic  houses. 

This  project  may  be  related  to  the  history  work.  A  number  of  pictures, 
carefully  mounted,  would  be  a  good  addition  to  the  history  department 
equipment. 

7.  Make  a  collection  of  woods. 

Obtain  pieces  of  different  kinds  of  wood;  saw  and  plane  them  all  the 
same  size;  insert  a  screw  eye  in  one  end;  and  label  each. 


246     PROTECTION  —  HOMES  AND  CLOTHING 

8.  Make  a  collection  of  leaves  from  softwood  and  hardwood  trees,  and  classify 
them.     Each  leaf  should  be  pressed,  mounted,  and  labeled.    Another  way 
would  be  to  make  blue-prints  of  the  leaves,  as  directed  on  page  161. 

9.  Make  plaster  mounts  of  scientific  subjects. 

See  directions  on  page  230.  Good  subjects  .would  be  airplanes,  auto- 
mobiles, engines,  great  scientists,  etc.  When  completed,  hang  them  on 
the  walls  of  the  schoolroom. 

10.  Mend  holes  in  plaster  walls  at  home. 

11.  Find  the  fuses  in  your  house.     Replace  a  burnt-out  fuse  with  a  new  one. 

Reports: 

1.  Materials  used  in  our  schoolhouse. 

Make  a  thorough  investigation  of  the  building  to  find  all  the  materials 
used.  Find  out  all  you  can  about  each  material,  and  explain  to  the  class. 

2.  What  the  public  buildings  of  our  town  or  neighborhood  are  made  of. 

Visit  and  inspect  each  building.  If  possible,  get  photographs  to  show 
your  classmates.  Any  facts  as  to  the  age  of  the  buildings,  their  cost,  etc., 
will  add  to  the  value  of  your  report.  Two  or  three  boys  may  work  on  this 
project. 

3.  A  visit  to  a  brickyard. 

Two  or  more  pupils  would  find  such  a  visit  instructive,  if  there  is  a 
brickyard  in  the  locality.  Explain  the  process  to  your  classmates. 

4.  Fire  fighting  in  our  town. 

Visit  a  fire  station.  Find  out  how  the  alarms  for  fire  are  given,  what 
the  apparatus  is,  how  quickly  it  is  ready,  etc.  Write  an  account  for  the 
school  paper. 

5.  How  we  are  protected  from  fire. 

Make  a  study  of  the  schoolhouse  from  the  standpoint  of  fire  protection, 
and  report  the  results  to  the  class. 

Reports  from  reading: 

Examine  the  list  of  books  at  the  end  of  this  project.     If  you  wish  to  look  up 
any  of  the  subjects  suggested  there,  consult  your  teacher. 

BOOKS  THAT  WILL  HELP  YOU 

Asia.     N.  B.  Allen.    Ginn  &  Co. 

"India,  the  Land  and  the  People." 
The  Book  of  Wonders.     Presbrey  Syndicate,  New  York. 

"  Story  in  a  Barrel  of  Cement." 
Diggers  in  the  Earth.     E.  M.  Tappan.    Houghton  Mifflin  Co. 

'  Down  in  the  Quarries." 

"Houses  of  Sand." 

"Bricks." 
Home  Life  around  the  World.   Mirickand  Holmes.  Houghton  MifBin  Co. 

A  children's  reader. 

Household  Science  and  Arts.     May  Morris.    American  Book  Co. 
Modern  Triumphs.     E.  M.  Tappan,  Editor.    Houghton  Mifflin  Co. 

Engineering  in  the  New  York  Subway. 
Shelter  and  Clothing.     Kinne  and  Cooley.     The  Macmillan  Co. 

A  textbook  in  Home  Economics. 
The  United  States.     I.  O.  Winslow.    D.  C.  Heath  &  Co. 

Building  stones. 
Government  pamphlets: 

Farmers'  Bulletins,  U.S.  Department  of  Agriculture: 

173.  Primer  of  Forestry,  Part  I. 


BUILDING  OUR  HOMES  247 

358.  Primer  of  Forestry,  Part  2. 
185.  Beautifying  the  Home  Grounds. 
461.  The  Use  of  Concrete  on  the  Farm. 
Bulletins  of  the  U.S.  Bureau  of  Forestry.   A  list  of  the  publications  may  be 

obtained  upon  application. 
Circulars  of  the  U.S.  Bureau  of  Standards. 
70.  Materials  for  the  Household. 

An  account  of  the  common  materials  used  in  houses.     Price  25  cents; 
free  if  obtained  through  Congressman. 
75.  Safety  for  the  Household. 

An  account  of  the  hazards  in  the  home,  with  directions  for  care  and 
treatment. 
Commercial  pamphlets: 

Booklets  published  by  the  Portland  Cement  Association,  1 1 1  West  Washing- 
ton St.,  Chicago: 
26.  Concrete  in  the  Country. 
115.  Concreting  in  Winter. 
129.  Tennis  Courts  of  Concrete. 

133.  Concrete  Septic  Tanks. 

134.  Concrete  Fence  Posts. 

135.  Small  Concrete  Garages. 

140.  Proportioning  Concrete  Mixtures. 

no.  Manual  Training  Course  in  Concrete. 
Automatic  Fire  Protection. 

General  IFire  Extinguisher  Co.,  Providence,  Rhode  Island. 
Magazine  articles: 

"  Bird  Houses."    Dearborn.   Scientific  American  Supplement,  July  29,  1916. 
"Teaching  Scientific  Forestry."     Baker.     Scientific  American  Supplement, 

July  29,  May  6,  1916. 


PROJECT  XII 
LIGHTING  OUR  HOMES 

A  well-lighted  house.  With  the  invention  of  glass  came  the 
greatest  improvement  in  lighting  buildings  man  has  ever  known. 
We,  who  live  in  houses  which  the  sunlight  can  freely  enter,  can- 
not realize  how  dark  and  unwholesome  the  dwellings  of  even  the 
wealthiest  were  a  few  hundreds  of  years  ago.  The  castles  of  the 
noblemen  of  the  middle  ages  had  stone  walls  with  a  few  narrow 
slits  to  admit  a  little  light.  In  this  respect  how  much  better  off 
even  poor  people  are  to-day  than  the  noblemen  were  then,  since 
we  can  receive  into  our  houses  the  light  of  day. 

In  this  project  we  shall  find  out  how  we  get  our  light  from  the 
sun,  and  how,  for  hours  of  darkness,  we  have  made  artificial  lights 
to  light  our  homes. 

Some  questions  to  answer.  Have  you  seen  fixtures  for  indi- 
rect electric  lighting?  When  you  have  finished  this  project,  you 
will  know  why  they  are  better  than  the  old  type  of  fixtures. 
How  many  questions  can  you  think  of  which  deal  with  lighting 
our  houses?  Here  are  a  few  samples.  Some  you  can  answer 
now.  Later  you  should  be  able  to  answer  them  all  correctly  and 
scientifically. 

What  is  the  advantage  of  a  fluted  glass  globe  on  an  electric 
light? 

Some  schools  have  roofs  made  largely  of  ribbed  glass.  Of 
what  advantage  are  they? 

How  are  electric  wires  covered  with  insulation? 

How  may  buildings  be  set  on  fire  by  electric  wires? 

Why  may  an  electric  light  suspended  from  the  ceiling  be  lighted 
by  pushing  a  button  in  the  wall? 

Why  are  bicycle  lamps  made  with  reflectors? 

INTRODUCTORY  PROBLEM  i :  How  DO  WE  GET  OUR  LIGHT? 
Directions: 

Part  I.  Daylight. 

What  furnishes  the  light  in  your  house  in  the  daytime?    Look  out  of  the 


LIGHTING  OUR  HOMES  249 

window.  Can  you  see  the  sun?  Try  as  many  windows  as  possible,  at 
home  or  in  the  schoolhouse.  From  how  many  can  you  see  the  sun? 

If  the  sun  shines  into  the  room,  how  large  a  space  is  lighted  directly  by 
it?  Is  the  rest  of  the  room  dark?  If  not,  do  you  know  what  causes  the 
light? 

If  the  sun  does  not  shine  directly  into  the  room,  can  you  explain  how  the 
room  is  lighted? 

Hold  some  object  in  the  direct  sunlight.  Observe  the  shadow.  Do  the 
rays  of  the  sun  travel  in  straight  lines  or  are  they  able  to  change  their 
direction? 

Part  2.  Artificial  light. 

Name  all  the  kinds  of  artificial  light  that  you  know.  What  kinds  do  you 
use  at  home?  What  kinds  are  used  at  school? 

Can  you  see  any  connection  between  these  "artificial  lights"  and 
sunlight? 

Part  3.  Other  lights. 

What  natural  lights  are  visible  at  night?  Do  you  know  whether  each 
gives  light  of  itself  or  is  lighted  by  reflection  from  something  else? 

Have  you  ever  seen  the  "Aurora  Borealis  " ?  Do  you  know  what  causes 
its  light? 

Name  the  cases  which  you  have  seen  where  sparks  appear  even  mo- 
mentarily. Can  you  account  for  them? 

Summary: 
What  are  the  principal  causes  of  light? 


PROBLEM  2:  How  is  LIGHT  REFLECTED? 

Directions: 

Hang  a  large  mirror  on  the  schoolroom  wall.  Let  one  pupil  state  what 
other  pupils  he  can  see  in  the  mirror.  Which  pupil  seems  to  him  to  be  in 
the  center  of  the  mirror?  Let  him  draw  an  angle  on  the  floor  near  the 
mirror,  one  line  pointing  towards  his  seat,  and  the  other  a  perpendicular 
line  from  the  center  of  the  mirror. 

Now  let  the  pupil  who  seemed  to  be  in  the  center  of  the  mirror  state 
whether  he  can  see  pupil  no.  I  when  in  his  seat.  If  he  can,  let  him  draw 
an  arrow  pointing  from  the  center  of  the  mirror  to  his  own  seat. 

Examine  the  angles  thus  made  on  the  floor.  Can  you  discover  anything 
about  the  reflection  of  light? 

Let  several  other  pupils  try  the  same  experiment. 

Conclusion: 
What  is  the  law  of  reflection? 


250    PROTECTION  —  HOMES  AND  CLOTHING 

PROBLEM  3:  WHERE  DOES  A  REFLECTED  IMAGE  APPEAR  TO  BE? 

Directions: 

Lay  a  mirror  on  a  table.  Place  an  ink  bottle,  an  open  book,  and  other 
objects  upon  it.  What  is  the  appearance  of  the  images? 

How  far  behind  the  mirror  does  the  top  of  the  ink  bottle  seem  to  be?  the 
top  of  the  book? 

Write  your  name  on  paper  while  looking  in  a  mirror.  W'hat  do  you 
observe? 

Summary: 

State  two  rules  as  to  the  appearance  of  a  reflected  image. 

PROBLEM  4:  How  is  A  ROOM  LIGHTED  BY  DIFFUSED  LIGHT? 

Directions: 

Part  i.  What  is  diffused  light? 

Set  a  mirror  upright  on  a  table.  Place  a  lighted  candle  in  front  of  it. 
(If  you  can  try  this  in  a  dark  room,  the  results  are  more  interesting.)  Can 
you  see  the  image  of  the  candle? 

In  place  of  the  mirror  use  a  piece  of  white  cardboard.  Can  you  see  the 
image  of  the  candle? 

Which  is  smoother,  the  mirror  or  the  cardboard?  Which  seems  to  light 
the  room  better? 

When  a  ray  of  light  strikes  anything  which  is  not  perfectly  smooth,  how 
is  it  reflected?  Does  a  smooth  surface  or  a  rough  surface  scatter  or  diffuse 
the  light  more? 

Part  2.  How  is  the  schoolroom  lighted  by  diffused  light? 

If  the  light  is  shining  directly  into  the  room,  name  the  objects  on  which 
the  direct  rays  fall. 

Follow  the  line  of  the  beam  of  light  to  where  it  strikes  the  floor.  Where 
does  the  reflected  ray  strike?  Where  is  it  reflected  from  there? 

Trace  the  reflection  of  several  rays  in  the  same  way. 

If  no  direct  rays  shine  into  the  room,  look  out  of  the  window  to  see  on 
what  the  sun  is  shining  directly.  How  many  of  the  objects  that  you  see  can 
send  reflected  rays  into  your  room?  Trace  the  reflection  from  object  to 
object  in  the  room. 

If  the  surfaces  on  which  the  rays  fall  are  rough,  how  are  the  rays  reflected? 
Summary: 

Explain  how  the  room  is  lighted  by  reflection  and  diffusion. 

PROBLEM  5:  WHAT  is  THE  PRINCIPLE  OF  REFRACTION? 
Directions: 

Look  at  the  goldfish  in  your  aquarium  from  above.  Now  look  at  them 
through  the  glass.  Do  they  appear  different?  Are  they  really  different? 


LIGHTING  OUR  HOMES  251 

Put  a  pencil  in  a  glass  of  water.  How  does  it  appear?  Can  you  hold 
the  glass  in  such  a  way  as  to  see  two  pencils,  apparently?  Are  these 
appearances  caused  by  changes  in  the  pencil  or  by  the  action  of  the 
light? 

Place  a  coin  in  the  bottom  of  a  deep  empty  dish.  Stand  so  you  can  just 
see  the  farther  edge  of  the  coin  over  the  edge  of  the  dish.  Let  another  pupil 
pour  water  into  the  dish.  What  happens? 

Questions  : 

1 .  In  order  for  you  to  see  the  goldfish,  through  what  substances  must  the 
rays  of  light  pass  when  they  are  reflected  from  the  goldfish's  body  to  your 
eyes? 

2.  Through  what  substances  must  the  rays  pass  which  are  reflected  from 
the  pencil  to  your  eyes? 

3.  Through  what  substances  must  the  rays  pass  which  are  reflected 
from  the  coin  to  your  eyes?    Are  all  these  substances  equally  dense  or 
compact  ? 

Summary : 

Sum  up  the  necessary  conditions  for  rays  of  light  to  be  bent,  or 
refracted. 

PROBLEM  6:  WHAT  ARE  THE  COLORS  IN  SUNLIGHT? 
Directions : 

Hold  a  piece  of  white  paper  in  the  direct  sunlight.  What  is  the  color  of 
the  light  which  shines  on  the  paper? 

Hold  a  glass  prism  in  the  sunlight.  What  happens?  How  many  colors 
can  you  distinguish? 

With  colored  crayons  draw  the  solar  spectrum  in  your  notebook. 

Conclusion  : 

WThat  colors  are  included  in  sunlight? 
Question  : 

Can  you  explain  the  formation  of  the  solar  spectrum  from  what  you 
know  of  refraction  ? 

PROBLEM  7:  To  FOCUS  THE  SUN'S  RAYS. 
Directions  : 

Secure  a  reading-glass  and  hold  it  in  such  a  way  that  all  the  rays  which 
pass  through  it  are  bent  inward  and  fall  on  one  small  spot  on  a  piece  of 
paper.  Can  you  set  fire  to  the  paper? 

Question : 

How  can  you  explain  the  result  of  this  experiment  by  the  principle  of 
refraction? 


252     PROTECTION  —  HOMES  AND  CLOTHING 

PROBLEM  8 :  To  MAKE  A  PINHOLE  CAMERA. 
Directions : 

Procure  a  cardboard  box  such  as  cereals  are  sometimes^sold  in.   Remove 
the  cover.     Cut  a  hole  in  the  bottom  and  paste  a  piece  of  tinfoil  over  it. 

Prick  a  small  pinhole  in  the  middle 
of  the  tinfoil.  Tie  thin  cloth  over 
the  open  end  of  the  box. 

Hold  the  "camera"  with  the 
pinhole  toward  a  candle  flame. 
The  results  are  more  interesting 
if  you  can  do  this  in  the  dark. 
What  appears  on  the  screen  of  the 
cloth?  Try  holding  the  camera 
in  different  positions  until  the 
image  is  plain. 
Question: 

How  does  the  image  differ  from 
FIG.  118.  A  pinhole  camera.  the  flame  itself? 

PROBLEM  9:  WHAT  is  THE  RELATION  BETWEEN  THE  AMOUNT  OF  LIGHT 

AND  THE  DISTANCE  FROM  THE  SOURCE? 
Directions: 

Place  a  candle  or  small  lamp  on  a  table.     One  foot  away  from  it  set  up 
a  screen  in  which  a  hole  one  inch  square  is  cut. 


FIG.  119.  Why  is  the  square  of  light  on  the  second  screen  larger  than  the  hole 
in  the  first? 

Place  a  larger  screen  upright  two  feet  away  from  the  candle.  Measure 
the  space  lighted  by  the  rays  of  light  which  pass  through  the  hole. 

Move  the  large  screen  three  feet  away  from  the  light.  How  large  a  space 
is  lighted?  Try  other  positions. 


LIGHTING  OUR  HOMES  253 

Conclusion: 

What  conclusion  can  you  make  about  the  relation  between  the  intensity 
of  light  and  the  distance  from  its  source? 

PROBLEM  10:  How  DOES  A  CANDLE  BURN  AND  GIVE  LIGHT? 

Directions: 

Examine  a  paraffin  candle.  By  melting  the  bottom,  fasten  the  candle 
upright  in  a  small  dish.  Apply  a  lighted  match  to  the  wick. 

What  happens  to  the  paraffin?  Watch  the  candle  as  it  burns.  Squeeze 
the  wick  with  two  iron  nails  or  a  forceps.  What  appears  on  the  metal? 
What  change  takes  place  in  the  paraffin  as  the  candle  burns? 

Blow  out  the  flame.  What  rises  from  the  wick?  While  it  is  still  rising, 
hold  a  lighted  match  about  one  inch  above  the  wick.  What  happens? 

Have  you  found  now  into  what  the  paraffin  must  be  changed  before  it 
burns? 

Hold  a  piece  of  cold  glass  in  the  flame  for  a  moment.  What  appears  on 
the  glass?  Where  did  it  come  from?  What  is  its  shape?  In  what  part 
of  the  flame  was  this  substance?  When  a  candle  burns  without  smoking 
what  happens  to  this  substance? 

Refer  to  problem  5  on  page  24  to  find  the  products  of  combustion  of  a 
candle. 

Summary: 

1.  How  must  the  paraffin  be  changed  before  it  burns? 

2.  What  are  the  glowing  particles  in  the  candle  flame? 

3.  What  are  the  two  products  of  combustion  when  a  candle  burns? 

PROBLEM  11:  How  DOES  A  KEROSENE  LAMP  GIVE  LIGHT? 
Directions: 

Light  an  ordinary  kerosene  lamp.  What  burns?  How  does  the  oil  rise 
to  the  flame? 

Use  the  lamp  with  and  without  the  chimney.  What  is  the  use  of  the 
chimney? 

Hold  two  lighted  matches  close  to  the  small  holes  on  the  burner.  What 
is  the  result?  What  is  the  use  of  the  holes  in  the  burner? 

Hold  a  cold  glass  in  the  flame.     What  causes  the  light  in  the  flame? 

Find  out  whether  the  products  of  combustion  are  the  same  as  in  the 
candle  flame. 

Summary: 

1.  Why  does  kerosene  give  light  when  it  burns? 

2.  Why  is  a  chimney  used? 

3.  What  are  the  products  of  combustion? 
Question: 

What  causes  a  kerosene  lamp  to  smoke? 


254    PROTECTION  —  HOMES  AND  CLOTHING 

PROBLEM  12:  How  DOES  A  GAS  MANTLE  INCREASE  THE  LIGHT  GIVEN  BY  A 

GAS  FLAME? 
Directions: 

Part  i.  Burn  gas  with  the  usual  "lava  tip."  Place  a  cold  object  in  the 
flame.  What  appears?  What  are  the  glowing  particles  in  the  light?  Do 
all  parts  of  the  flame  give  light?  How  far  must  the  stop-cock  be  turned 
to  furnish  gas  enough  to  give  the  best  possible  light? 

Part  2.  Replace  the  tip  with  a  mantle  burner  and  chimney.  Light  the 
gas.  What  causes  the  light?  What  is  the  use  of  the  chimney?  How  far 
must  the  stop-cock  be  turned  to  furnish  gas  enough  to  give  the  best  pos- 
sible light? 

Compare  the  intensity  of  light  given  by  the  two  burners. 

Summary: 

What  advantages  has  a  mantle  light  over  an  open  flame? 

PROBLEM  13:  WHAT  CAUSES  AN  INCANDESCENT  ELECTRIC  LAMP  TO  GIVE 

LIGHT? 
Directions: 

Part  i.  How  does  an  electric  current  affect  wire? 

Connect  the  binding  posts  of  a  dry  cell  by  means  of  a  short  piece  of  Ger- 
man silver  wire.  Feel  the  wire.  What  is  the  effect? 

Try  a  piece  of  German  silver  wire  of  smaller  diameter,  but  the  same 
length.  What  is  the  effect? 

Try  a  piece  of  copper  wire  the  same  length.  Which  of  the  three  wires 
becomes  most  heated?  Which  offers  the  greatest  resistance  to  the  passage 
of  the  electric  current? 

Part.  2.  What  is  the  construction  of  an  incandescent  lamp? 
From  observation  and  investigation  find  out  the  parts  of  the  lamp. 

Part  3.  What  causes  the  light  in  the  incandescent  bulb? 

Connect  a  small  bulb  such  as  is  used  in  a  flash-light  with  the  binding- 
posts  of  a  dry  cell.  What  is  the  effect?  In  how  many  ways  may  the  light 
be  turned  off  and  on? 

Summary: 

State  two  necessary  conditions  for  an  incandescent  lamp  to  give  light. 

Questions: 

1.  What  may  cause  the  insulation  of  an  electric  wire  to  burn? 

2.  Why  does  an  electric  light  go  out  if  the  filament  breaks? 

PROBLEM  14:  To  MAKE  A  SIMPLE  ELECTRIC  CELL. 

Directions: 

Place  some  water  in  a  glass.  Add  a  few  drops  of  sulphuric  acid.  Place 
clean  strips  of  copper  and  of  zinc  in  the  glass  on  opposite  sides,  and  connect 


LIGHTING  OUR  HOMES 


255 


them  by  a  copper  wire,  as  shown  in  the  diagram.  Hold  a  small  compass 
near  the  wire.  If  the  needle  is  turned,  an  electric  current  is  passing 
through  the  wire.  What  can  you 
observe  in  the  liquid?  Is  chemi- 
cal action  going  on? 

Break  the  connection  between 
the  metal  strips  by  removing  the 
wire  from  one  of  the  binding- 
posts.  Can  you  detect  any  dif- 
ference in  the  chemical  action? 
Questions: 

1.  What  kind  of  energy  causes 
the  formation  of  bubbles  in  the 
liquid? 

2.  What  kind  of  energy  causes 
a    deflection    of    the    magnetic 
needle  when  it  is  held  near  the 
wire? 


PROBLEM  15 :  To  SEE  HOW  A  DRY 
CELL  WORKS  AND  TO  STUDY 
ITS  PARTS. 

Directions: 

Operate  by  means  of  a  fresh 
•    '      11  j  •  FIG.  1 20.    A  simple  electric  cell.    The  parts 

dry  cell  as  many  devices  as  possi-     are  designated  in  £*te*>  symbols  Cu>  ^ 

ble  such  as  an  electric  bell,  flash-     Zn,  zinc;  H2O,  water,  H2SO4,  sulphuric  acid. 

light,  buzzer,  toaster,  etc. 
Take  apart  an  old  dry  cell  and  examine  its  structure.    Find  the  zinc  can. 

Has  the  chemical  action  caused  the  zinc  to  be  worn  away?  Find  the  car- 
bon rod.  How  can  it  be  connected 
with  an  outside  circuit?  Remove 
some  of  the  paste.  Is  this  actu- 
ally a  "dry"  cell? 

Question: 

What   advantages    have    dry 
cells  over  wet  cells? 

PROBLEM  16:  To  CONNECT  CELLS 
TO  FORM  A  BATTERY. 

Directions: 

FIG.  121.  Cells  connected  in  parallel  and  in  „  ,      .        ,         ,      .          , 

series  Connect  by  insulated  wires  the 

carbon  of  a  dry  cell  to  the  zinc  of 
a  second,  the  carbon  of  the  second  to  the  zinc  of  a  third,  and  the  carbon 


256    PROTECTION  —  HOMES  AND  CLOTHING 

of  the  third  to  a  circuit  containing  an  electric  light  and  a  switch.  Turn 
on  the  switch.  What  is  the  effect?  This  battery  is  said  to  be  connected 
in  series. 

Connect  the  carbons  of  all  three  cells  to  a  wire  which  has  in  its  circuit 
an  electric  light  and  a  switch.  Connect  the  zincs  of  all  three  cells  with  the 
circuit.  See  the  diagram.  What  is  the  effect  when  the  circuit  is  com- 
pleted by  turning  the  switch?  This  battery  is  said  to  be  connected  in 
parallel. 

How  our  houses  are  lighted  by  the  sun.  The  sun  might  shine 
with  great  intensity  on  the  outside  of  our  houses,  yet  not  a  ray 
of  light  might  enter.  We  have  windows  to  admit  the  light.  Any 
substance  which  allows  light  waves  to  pass  through  it  and  show 
the  form  of  objects  is  transparent.  Glass,  air,  and  water  are 
transparent.  Wood,  stone,  brick,  and  plaster  are  opaque;  they 
do  not  allow  light  waves  to  enter.  If  you  can  see  light  through  a 
substance,  but  cannot  easily  distinguish  objects  through  it,  the 
substance  is  translucent.  Celluloid,  ground  glass,  and  light-col- 
ored window  shades  are  translucent. 

Reflected  light.  Perhaps  the  sun  never  shines  directly  into  the 
north  rooms  of  your  house,  yet  they  are  not  dark.  When  light 
waves  strike  an  object,  three  things  may  happen  to  them.  They 
may  be  absorbed  by  the  object;  they  may  be  transmitted,  or  pass 
through;  or  they  may  be  turned  back,  or  reflected.  When  the 
light  waves  strike  a  pane  of  window  glass,  all  three  things  happen. 
The  glass  becomes  somewhat  warm  to  the  touch,  because  when 
the  rays  are  absorbed  some  of  the  light  energy  is  transformed  to 
heat  energy.  Light  shines  into  the  room,  because  glass  trans- 
mits the  waves.  Some  light  waves  are  reflected;  perhaps  you 
have  noticed  a  house  with  its  windows  lighted  by  the  reflected 
rays  of  the  setting  sun. 

In  the  case  of  the  north  windows  of  your  house,  the  direct  rays 
of  the  sun  never  reach  them.  Yet  light  is  admitted.  This  is 
because  light  is  reflected  from  some  objects  outside  the  window. 
Why  do  photograph  galleries  usually  have  north  windows? 

As  you  know  from  observing  shadows,  light  always  travels  in 
straight  lines.  It  cannot  turn  a  corner.  It  can,  however,  be 
reflected  at  an  angle.  If  you  drive  a  tennis  ball  obliquely  against 
a  wall,  it  will  not  return  toward  your  racquet,  but  will  be  reflected 


LIGHTING  OUR  HOMES 


257 


at  an  angle.  In  somewhat  the  same  way  light  rays  are  reflected. 
We  call  the  angle  at  which  the  light  strikes  the  surface  the  angle 
of  incidence.  It  is  equal  to  the  angle  of  reflection.  Study  the  dia- 
gram to  understand  what  this  statement  means. 

Reflection  from  mirrors.  Reflection  takes  place  from  almost 
all  surfaces,  either  rough  or  smooth.  But  the  smoother  the  sur- 
face, the  clearer  the  image  is.  By  " image"  we  mean  the  picture 
that  we  see  of  the  real  object. 
A  baby  cannot  distinguish  be- 
tween an  image  and  a  real  thing. 
You,  however,  can  understand 
that  you  see  an  image  of  your- 
self in  a  mirror  or  other  shiny 
surface  because  rays  which 
started  from  the  sun  are  reflected 
from  surface  to  surface  until  they 
strike  your  body ;  then  they  are 
reflected  from  your  body  to  the  mirror,  and  back  again  to  the 
retinas  of  your  eyes. 

Two  laws  of  reflection  are  that  an  image  appears  to  be  as  far 

behind  a  mirror  as  the  ob- 
ject is  in  front  of  it;  and 
that  the  image  is  reversed. 
For  example,  when  you 
look  in  a  mirror,  your 
right  hand  appears  to  be 
the  left  hand  of  the 


FIG.  122.  The  angle  of  incidence  is  equal 
to  the  angle  of  reflection  .- 


image. 

Diffused  light.  Dif- 
fused light  is  scattered 
light.  Light  rays  may  be 
scattered  or  spread  in  all 
directions  for  two  rea- 
sons; because  they  are 
reflected  in  many  differ- 
ent directions,  or  because 
they  pass  through  translucent  substances.  Let  us  consider  the 


FIG.  123.  A  comparison  of  objects  and  their  images. 
Notice  that  in  the  image  the  handle  of  the  candle- 
stick is  turned  towards  you,  while  on  the  object  it  is 
turned  away. 


258     PROTECTION  —  HOMES  AND  CLOTHING 

first  case.  When  several  rays  of  light  from  one  source  strike  a 
perfectly  smooth  surface,  like  a  mirror  or  a  clear  pool  of  still 
water,  they  are  practically  all  reflected  in  the  same  direction. 
See  problem.  We  can  see,  therefore,  a  distinct  image  of  the 
object  from  which  the  rays  came.  If  the  rays  of  light  strike  a 
rough  surface,  like  a  rough  plaster  wall,  each  ray  is  reflected  in  a 
slightly  different  direction.  We  cannot  see  any  distinct  image, 
but  the  rays  are  so  scattered  as  to  light  up  the  entire  room.  Our 
rooms  would  be  very  poorly  lighted  if  it  were  not  for  the  reflec- 
tion of  diffused  light  through  the  windows  and  from  the  walls. 

Reflection  of  light  prevents  the  shade  of  trees  and  houses  from 
being  very  dark.  On  cloudy  days  the  light  of  the  sun  is  reflected 
from  one  tiny  drop  of  moisture  in  the  clouds  to  another,  until  it 
finally  is  sent  to  the  earth.  The  reflection  from  dust  particles 
in  the  air  gives  the  sky  its  blue  color. 

Refracted  light.  We  have  found  that  light  travels  in  straight 
lines,  that  it  cannot  turn  a  corner,  but  that  it  can  be  reflected, 

or  turned  back.  Now  we  shall 
find  that  a  ray  of  light  can  be 
bent,  or  refracted. 

If  you  were  riding  in  a 
hydro-aeroplane,  you  would 
start  by  skimming  through 
the  water,  then  you  would 
rise  into  the  air,  and  fly  even 
faster.  At  the  end  of  your 
flight  you  would  take  to  the 
water  again,  and  your  speed 
would  slow  down.  In  some- 
what the  same  way  a  ray  of  light  may  pass  through  water  or  glass. 
When  it  leaves  the  air  to  enter  the  water  or  the  glass,  its  speed 
slows  down.  If  it  enters  them  at  an  angle,  the  ray  is  bent  aside, 
because  it  meets  with  greater  resistance  in  the  denser  substances. 
We  are  all  familiar  with  some  of  the  peculiar  results  of  this 
bending  aside  of  the  rays.  An  object  in  a  jar  of  water  seems 
larger  than  it  really  is.  A  fish  that  you  can  see  nibbling  your 
bait  looks  much  bigger  than  when  you  have  finally  succeeded  in 


FIG.  124.  Refraction  causes  the  coin*  to  ap- 
pear to  change  position  when  water  is  poured 
into  the  dish.  (See  problem  5.) 


LIGHTING  OUR  HOMES 


259 


pulling  it,  struggling,  from  the  water.     What  other  examples  of 
refraction  can  you  mention? 

The  colors  in  sunlight.  The  rainbow  is  a  result  of  refraction  of 
the  sun's  rays.  Sunlight,  while  apparently  white,  is  really  com- 
posed of  six  colors,  the  spectrum  colors, 
—  red,  orange,  yellow,  green,  blue,  and 
violet.  The  waves  of  all  these  colors  are 
of  different  lengths.  The  red  waves  are 
longest,  the  orange  next  longest;  then  yel- 
low, green,  blue,  and  violet,  which  are  the 
shortest  waves.  When  the  waves  enter 
a  denser  substance  as  when  they  pass  from 
the  air  into  a  glass  prism,  the  shortest 
waves  are  bent  aside  the  most,  the  next 
shortest  the  next,  and  so  on.  So  the 
different  rays  are  separated  to  form  a 
spectrum.  In  the  case  of  the  rainbow, 
the  waves  of  light  enter  a  drop  of  water, 
and  when  they  leave  it  again  are  sepa- 
rated to  show  the  different  colors. 

Why  anything  has  color.  Have  you 
noticed  that  at  night  colors  disappear? 
Then  an  object  is  merely  light  or  dark. 
All  color  is  due  to  sunlight,  as  its  source, 
light  may  be  either  reflected,  transmitted,  or  absorbed.  The 
different  colors  in  light  may  act  differently.  The  white  paper 
of  this  page  reflects  all  the  colors  back  to  your  eyes.  The  black 
letters  absorb  all  the  colors.  Green  leaves  reflect  the  green 
waves  to  your  eyes  and  absorb  all  the  other  colors. 

The  wall-papers  in  your  rooms  have  a  great  effect  on  the 
amount  of  light  in  the  room.  If  they  are  "  light "  in  color,  they 
reflect  nearly  all  the  rays  that  fall  upon  them.  If  they  are 
"  dark,"  they  absorb  nearly  all  the  rays.  For  this  reason  care 
should  be  exercised  in  the  choice  of  wall-papers  to  see  that  they 
are  adapted  to  the  uses  to  which  the  various  rooms  are  put. 

A  lens.  We  have  found  that  a  drop  of  water  or  a  prism  can 
separate  the  rays  of  light.  A  lens  can  bring  them  to  a  point, 


FIG.  125.  A  lens  for  an  auto- 
mobile headlight.  The  light 
rays  are  so  bent  by  refraction 
that  they  light  a  large  area  in 


You  remember  that 


260    PROTECTION --HOMES  AND  CLOTHING 

or  focus  them.  The  reason  is  the  same;  the  rays  are  refracted 
when  they  go  from  one  substance  to  another. 

A  reading-glass  bends  the  rays  from  the  letters  on  this  page 
so  that  when  they  reach  our  eyes  they  seem  to  have  come  from 
letters  which  are  nearer  and  larger.  You  can  use  a  reading-glass 
to  focus  the  sun's  direct  rays  to  a  point.  So  many  rays  beating 
upon  the  same  spot  may  produce  enough  heat  to  set  fire  to  paper 
or  cloth  or  light  "  kindling." 

A  camera.  A  "pinhole  "  camera  can  be  made  without  using  a 
lens.  The  rays  of  light,  passing  through  the  hole,  fall  upon  a 

screen  of  some  kind  and 
produce  a  faint,  inverted 
image. 

When  a  double  convex 
lens,  a  kind  of  lens  that 
bulges  in  the  center,  is  used 
in  the  opening,  the  rays  of 
light  reflected  from  outside 

FIG.  126.  A  camera,  showing  the  lens  and  how  the          . 

image  is  formed.  objects  enter  the  lens  and 

form  a  bright  image  on  a 

screen  placed  in  the  proper  position.  The  image  is  inverted 
and  is  much  smaller  than  the  real  objects.  Study  the  dia- 
gram. 

The  development  of  modern  photography  has  all  depended  on 
the  discovery  that  light  causes  a  chemical  action  on  silver  salts. 
A  white  silver  salt,  when  exposed  to  the  light,  turns  dark.  The 
film .  or  plate  in  a  camera  is  coated  with  gelatin  which  contains 
a  silver  salt,  usually  silver  bromide.  The  film  is  placed  at  just 
the  right  place  to  receive  the  focused  rays  from  a  lens.  When 
you  take  a  "snapshot"  the  shutter  opens  for  a  fraction  of  a 
second.  The  light  that  enters  changes  the  silver  salt  on  the 
film.  The  many  rays  reflected  from  the  surface  of  the  water 
through  the  lens  cause  the  part  of  the  film  where  those  rays 
fall  to  turn  dark  quickly,  while  the  fewer  rays  reflected  from 
the  sides  of  the  canoes  cause  less  chemical  action  on  the  part  of 
the  film  where  those  rays  fall. 

The  film  is  " developed"  by  chemicals  and  forms  a  negative. 


LIGHTING  OUR  HOMES 


261 


The  negative  is  dark  where  the  object  was  light  and  light  where 
the  object  was  dark. 

The  print,  or  positive,  is 
made  by  allowing  light  to 
pass  through  the  negative 
to  paper  which  is  sensitive 
to  light  because  it  is  coated 
with  a  silver  salt.  Less 
light  can  pass  through  the 
dark  parts  of  the  negative 
than  through  the  light 
parts.  Therefore  what  was 
dark  on  the  negative  ap- 
pears light  on  the  positive, 
and  what  was  light  on  the 
negative  appears  dark  on 
the  positive. 

The  human  eye.  The 
most  wonderful  camera  in 
the  world  is  the  human  eye. 
The  light  enters  through 
the  pupil,  which  is  a  hole 

which  can  be  made  larger  FIG.  127.  A  negative  and  a  positive.  Notice  that 
Or  smaller  when  necessary  what  is  dark  in  the  negative  is  light  in  the  positive. 
.  ,  ,  ,  .  (Courtesy,  Eastman  Kodak  Co.) 

by  the  contracting  or  en- 

larging of  the  colored  part  of  the  eye,  the  iris.  The  rays  of 

light  then  pass  through 
the  crystalline  lens,  and  are 
focused  in  the  back  of  the 
eye  on  a  sensitive  layer  of 
nerve  tissue  called  the  re- 
tina. From  the  retina  the 
optic  nerve  leads  to  the 
brain  where  impressions 
of  light  are  registered. 


FIG.  128.  The  eye  and  its  connections. 
(From  Woods  Hutchinson's  Handbook  0}  Health) 


Glasses  are  needed  by  some 
to  enable  ^  of 


262     PROTECTION  —  HOMES  AND  CLOTHING 

light  to  be  focused  properly.  These  people  need  glasses  because  their  eyes 
are  so  made  that  the  rays  of  light  instead  of  being  focused  upon  the  retina 
tend  to  be  focused  either  in  front  of  the  retina  or  behind  it.  For  this  reason 
different  eyes  need  different  kinds  of  glasses.  Perhaps  there  are  no  organs 
in  the  body  that  are  more  often  abused  than  the  eyes.  Many  people  suffer 
from  eye-strain  without  realizing  it.  This  is  because  of  the  fact  that  there 
are  little  muscles  attached  to  the  lenses  of  the  eyes  by  means  of  which  the 
lenses  may  be  made  thicker  or  longer.  These  muscles  may  be  tired  out 
or  strained  if  you  do  not  have  glasses  to  help  them.  This  strain  often  re- 
sults in  headaches  and  in  disturbance  in  other  parts  of  the  body  such  as  the 
stomach  and  back.  If  you  suffer  any  discomfiture  after  using  the  eyes  for 
an  hour  or  so,  you  should  consult  an  oculist  to  find  out  whether  or  not 
you  need  glasses. 

The  intensity  of  light.  One  way  of  abusing  the  eyes  is  to  write 
or  read  in  a  poor  light.  If  you  have  tried  problem  9  on  page 
252,  you  have  found  that  the  intensity  of  light  diminishes  very 
rapidly  with  distance.  If  you  sit  twice  as  far  away  from  a  lamp 
as  your  sister,  you  receive  but  one  fourth  as  much  light.  If  you 
are  four  feet  away,  while  she  is  but  one  foot  away,  she  receives 
sixteen  times  as  much  light  as  you  do. 

Natural  and  artificial  lighting.  By  the  term  natural  lighting 
we  mean  light  received  directly  from  the  sun.  The  sun  is,  how- 
ever, the  real  source  of  all  our  light  except  the  small  amount 
which  comes  from  the  stars.  Artificial  light  is  usually  produced 
through  the  oxidation  or  burning  of  substances  such  as  wood, 
coal,  oil,  or  gas.  These  substances  have  energy  stored  in  them 
which  came  originally  from  the  sun.  (See  page  216.) 

Candle-light.  Our  ancestors  used  candles  as  almost  their  only 
source  of  artificial  light.  We  use  them  only  when  we  wish  a  soft 
light,  as  at  dinner  sometimes,  in  our  bedrooms,  and  for  religious 
ceremonies  and  festivals. 

A  candle,  whether  it  is  made  of  paraffin,  wax,  o;r  tallow,  con- 
tains the  same  elements,  carbon,  hydrogen,  and  oxygen.  We  know 
from  our  study  of  air  and  fire  that  the  candle  will  not  burn  with- 
out the  help  of  oxygen  from  the  air.  So  we  know  that  the  car- 
bon unites  with  oxygen  to  form  the  colorless  gas  carbon  dioxide, 
and  the  hydrogen  unites  with  oxygen  to  form  water. 

Solid  paraffin  does  not  burn  easily.     First  it  melts  and  creeps 


LIGHTING  OUR  HOMES 


263 


FIG.  129.  A  candle  flame. 
I,  the  faintly  luminous  man- 
tle; 2,  the  bright  yellow  lum- 
inous region;  3,  the  unburned 
gases;  4,  the  blue  region  at 
the  base. 


up  the  wick  by  capillary  action.  (See  page  134.)  The  burning 
wick  is  hot  enough  to  turn  the  melted  paraffin  to  a  vapor,  and  not 
until  then  does,  the  paraffin  itself  catch 
fire.  So  in  a  candle  flame  we  really  see 
a  gas  or  vapor  burning. 

Each  part  of  the  rising  column  of 
vapor  cannot  get  an  equal  amount  of 
oxygen.  The  outside  of  the  column  burns 
very  quickly,  forming  at  once  the  color- 
less carbon  dioxide  and  water.  The 
particles  of  vapor  farther  inside  the  flame 
cannot  burn  so  fast.  Each  particle  of 
carbon  glows  for  a  second  before  it  is 
burned  completely.  It  is  the  glowing  car- 
bon particles  that  cause  the  flame  to  give 
light.  Study  the  diagram  to  see  the  parts 
of  a  candle  flame. 

A  kerosene  lamp.  Have  you  heard  of 
whale-oil  lamps  ?  Until  about  sixty  years 
ago  they  were  the  best  artificial  light  known.  Then,  in  1858, 
came  kerosene,  from  petroleum,  which  had  been  waiting,  stored 
up  deep  in  the  earth's  crust,  until  man  should  realize  its  value 
and  bore  wells  to  obtain  it. 

A  kerosene  lamp  must  have  a  bowl  for  the  oil  and  a  wick;  it 
usually  has  also  a  chimney  and  a  burner. 

If  you  made  the  lamp  suggested  on  page  123,  you  learned  that 
soil  might  act  as  a  wick.  The  wick  is  useful  to  enable  the  oil 
to  creep  by  capillary  action  up  to  where  the  heat  from  a  match 
may  change  it  into  a  gas.  As  in  the  candle,  the  material  that 
really  burns  is  a  gas.  Like  the  candle,  too,  the  kerosene  contains 
carbon,  hydrogen,  and  oxygen.  The  glowing  carbon  particles 
furnish  the  light,  and  the  products  of  combustion  are  carbon 
dioxide  and  water. 

The  burner  and  chimney  are  useful  in  furnishing  a  steady  sup- 
ply of  air  to  yield  its  oxygen,  and  in  preventing  cross  currents  of 
air  which  cause  a  flickering  flame. 

Gas-lighting.     Illuminating  gas  is  usually  a  mixture  of  gases 


264     PROTECTION  --HOMES  AND  CLOTHING 


cyiu 


produced  from  coal,  petroleum,  etc.  When  you  study  chemistry 
you  will  find  out  just  how  the  different  kinds  are  made.  However 

it  is  made,  it  resembles  the 
paraffin  candle  and  the 
kerosene  oil  in  consisting 
of  the  elements  carbon, 
hydrogen,  and  oxygen. 
When  it  burns,  the  car- 
bon is  oxidized  to  form 
carbon  dioxide,  and  the 
hydrogen  forms  water. 

FIG.  130.  A  gas-meter  index  rea,  The    gas  .g  piped  tQ  yQm 

(Courtesy,  Bureau  of  Standards,  Washington.)  house  from  the  city  tanks, 

and    its    escape    is     pre- 

vented by  stop-cocks.  The  amount  you  use  in  your  house  is 
measured  by  a  gas-meter.  Learn  to  read  the  meter,  so  that  you 
may  detect  any  leak  in  it  candies  \ 

or  any  mistake  in  the  gas- 
bill.  • 

Two  types  of  gas-burn- 
ers are  in  use,  the  open- 
flame  burner,  and  the  man- 
tle burner.  The  open-flame 
burner  allows  gas  to  burn 
in  the  air.  The  more  air  is 
admitted  to  the  flame, 
the  less  light  is  given,  be- 
cause oxidation  is  carried 
on  too  fast  to  allow  the 


Kerosene  Flan 


Gas  Open  Flame  " 
Gas  Mantle 
Carbon  £/fee//7c 
"Gem"  Elccrr/c 
Tunasfen  Ek 


5         (O        IS        20       25        3O       35 
Cost  of  IOOO  candle-hours  in  cents 


FIG.  131.  Relative  cost  of  producing  a  given 
amount  of  light  by  various  illuminants  at  usual  prices. 
Costs  are  based  on  the  following  prices:  candles, 


Carbon    particles   tO  glow.     I2  cents  per  pound;  kerosene,  15  cents  per  gallon; 


A  Bunsen  burner  admits 
air  to   the  inside   of  the 


gas,  $i  per  1,000  cubic  feet;  electricity,  10  cents  per 
kilowatt  hour.  The  solid  lines  represent  cost  of  fuel 
or  of  current,  the  shaded  parts  the  cost  of  the  mantles 


flame,  so  the  carbon  par-    and  bulbs-  Where  Prices  are  different  from  those 

.  ,.       ,       given  above,  costs  will  be  correspondingly  different. 

tides  are  quickly  oxidized. 

.  (Courtesy,  Bureau  of  Standards,  Washington.) 

An  ordinary   burner   ad- 
mits no  air  to  the  center  of  the  flame,  and  the  carbon  is  oxidized 
slowly  enough  to  glow. 


LIGHTING  OUR  HOMES 


265 


Mantle  burners  are  so  much  more  efficient  than  open  flames 
that  they  are  in  general  use.  A  mixture  of  gas  and  air  is  admitted 
inside  the  mantle,  where  it  burns  with  a  blue  flame,  producing  no 
light,  but  much  heat.  The  light  is  caused  by  a  coating  on  the 
mantle  made  of  a  mineral  substance  which  cannot  burn,  but  is 
heated  to  incandescence  or  glowing. 

Electric  lights.  The  most  important  development  in  lighting 
our  houses  has  come  as  a  result  of  our  knowledge  of  electricity 
and  electrical  energy. 
We  have  likened  (see 
page  236)  the  electric 
current  in  a  wire  to  the 
flow  of  water  in  a  pipe. 
The  electrical  pressure 
causes  the  current  to 
pass.  Two  common  ways 
of  producing  electrical 
pressure  are  by  means  of 
electric  cells  and  dyna- 
mos. A  pocket  flash- 
lamp  can  give  a  good 
light  as  a  result  of  the 
energy  in  an  electric  cell. 
The  current  which  flows 
through  the  lights  in  our 
houses  is  caused  by  dy- 
namos, which  we  shall 
consider  in  the  project 
on  transportation. 

Electric  cells.  A  very 
simple  electric  cell  may 
be  made  by  using  a  strip  of  copper  and  a  strip  of  zinc  in  dilute 
acid.  When  these  two  strips,  or  poles,  are  joined  by  a  wire  we  can 
see  that  chemical  action  goes  on  in  the  cell,  and  a  current  passes 
through  the  wire.  A  cell  of  this  kind  becomes  useless  in  a  few 
minutes  because  the  copper  becomes  covered  with  bubbles  which 
prevent  the  chemical  action  from  continuing.  An  electric 


FIG.  132.  A  gravity  cell.  The  current  passes  from 
the  positive  pole  (-J-)  through  the  wire  to  the  negative 
pole(-). 


266     PROTECTION  —  HOMES  AND  CLOTHING 


Scrnd 


cell  shows  chemical  energy  being  transformed   into   electrical 
energy. 

Telegraph  companies  use  a  type  of  electric  cell  called  the  gravity  cell.  A 
battery  jar,  in  the  bottom  of  which  crystals  of  copper  sulphate  are  placed, 
is  filled  with  water.  A  specially  shaped  piece  of  copper  is  placed  in  the 

bottom  of  the  jar  and  a  piece 

-Do wet  Cap  of   zinc   is    supported    near 

/Vut  the  top  of  the  liquid.   Both 

Acorn  Heed  Pod  metals  are  connected  with 
wires  to  form  a  circuit.  A 
few  drops  of  sulphuric  acid 
are  added  to  the  water. 
Chemical  action  continues 
for  a  long  time  in  a  cell  of 
this  type. 

The  most  common  wet 
cell  is  made  from  sal-ammo- 
niac dissolved  in  water. 
Zinc  and  carbon  are  used 
for  poles. 

The  most  convenient  cell 
to  use  is  the  "dry"  cell.  It 
consists  of  a  zinc  can  which 
contains  a  carbon  rod.  Be- 
tween the  rod  and  the  walls 
of  the  can  is  a  paste,  the 
most  important  material  of 
which  is  sal-ammoniac.  The 
chemical  action  causes  the 
zinc  to  be  eaten  away  in 
time  and  then  the  cell  is 
said  to  be  dead. 


Pu/pboord  L  /ning 


Carbon  E/ec/rode 


M/x 


Z/nc  Cor) 


Pulpboord  Bottom 


FIG.  133.  A  section  of  a  dry  battery.  The  "mix" 
is  a  black,  sandy  mass  composed  of  sal-ammoniac, 
carbon  powder,  and  other  chemicals.  The  carbon 
electrode  and  the  mix  comprise  the  positive  pole. 
What  is  the  negative  pole? 

(Courtesy,  National  Carbon  Co.) 


Some  flash-lights  contain  more  than  one  cell.  A  combination 
of  cells  is  called  a  battery.  The  cells  are  so  arranged  that  the  cur- 
rent travels  through  the  wires  from  carbons  to  zincs  and  through 
the  cells  from  zincs  to  carbons.  Batteries  for  doorbells,  gasolene 
engines,  telephones,  and  automobiles  are  thus  arranged  in  series. 
Street  lamps  are  usually  arranged  in  this  way.  If  one  lamp 
breaks,  the  current  is  broken,  and  none  of  the  tamps  give  light. 

In  our  houses  we  wish  to  be  able  to  use  the  lights  independently. 
They  are  therefore  arranged  in  parallel.  The  electric  current 


LIGHTING  OUR  HOMES 


267 


enters  the  house  by  one  main  wire.  Branches  of  this  wire  supply 
each  room,  but  all  unite  and  leave  the  house  by  one  main  wire. 
Turning  a  switch  in  one  room  allows  the  current  to  pass  through 
the  lamps  in  that  room  only. 

Cells  may  also  be  arranged  in  parallel.  The  current  flows  from 
all  the  carbons  through  the  circuit  to  all  the  zincs,  and  back  to 
the  carbons  through  the 
cells.  The  current  through 
a  battery  arranged  in  par- 
allel is  greater  than  that 
through  a  battery  ar- 
ranged in  series. 

Conductors  and  insu- 
lators. Certain  sub- 
stances allow  an  electric 
current  to  pass  through 
them  easily;  they  are 
called  conductors.  All 
metals  are  good  conduc- 
tors. Other  substances 
which  do  not  allow  the 
current  to  pass  are  called 
insulators.  Wires  are  in- 
sulated by  being  covered 
with  rubber,  cloth,  or 
paper.  Glass  insulators  T 

are  used  On  lightning  rods     FlG-  X34-  A  diagram  to  show  how  electric  lights  are 
.  arranged  in  parallel. 

and  telegraph  wires. 

Switches.  A  switch  is  used  to  close  or  complete  a  circuit.  It 
is  so  made  that  pressing  a  button  or  turning  a  knob  brings  two 
metal  pieces  into  contact  and  allows  the  electric  current  to  flow. 

Fuses.  No  substance  is  a  perfect  electrical  conductor.  The 
current  meets  with  some  resistance  to  its  flow,  no  matter  what 
kind  of  material  it  passes  through.  Certain  substances  offer 
more  resistance  than  others.  Under  such  circumstances,  elec- 
trical energy  is  transformed  into  heat  and  the  wires  may  become 
so  hot  as  to  glow  or  melt. 


+ 

4 

( 

2  ^2.0 

<X>00 

- 

+ 

0*00 

+ 

- 

<3 

0000 

~r-      0 

11 

268     PROTECTION  —  HOMES  AND  CLOTHING 


A  fuse  is  a  protective  device  which  depends  upon  this  prin- 
ciple. When  the  current  enters  a  house  it  must  pass  through  a 
fuse  plug  which  contains  a  mixture  of  lead  and  tin  or  other  metals. 
If  the  current  becomes  too  great  for  safety  the  metal  melts  and 
thus  breaks  the  connection. 

An  incandescent  lamp.  The  usual  electric  light  bulb  depends 
upon  the  principle  that  a  substance  may  offer  enough  resistance 
to  the  passage  of  the  current  to  become  white  hot.  It  consists  of 
a  glass  bulb  from  which  practically  all  the  air  has  been  removed. 
Two  pieces  of  platinum  wire  are  sealed  into  the  base,  which  is  of 
plaster  of  Paris  with  a  brass  covering  which  can  be  screwed  into 
a  socket.  Connecting  the  two  platinum  wires  inside  the  bulb 

is  a  fine  thread  composed 
either  of  specially  pre- 
pared carbon  or  of  a  rare 
metal  called  tungsten. 
When  the  circuit  is  closed, 
the  current  meets  with  so 
much  resistance  in  pass- 
ing through  the  fine  thread 
that  it  glows  or  becomes 
incandescent. 

Edison  and  the  electric 
light.  America's  greatest 
inventor,  Thomas  A.  Edi- 
son, made  the  first  incan- 
descent lamp.  The  story 
of  its  invention  is  the 
story  of  persistent,  long,  and  hard  work.  He  already  knew 
about  the  electric  arc  light,  in  which  light  is  produced  by  an 
electric  current  flowing  across  a  gap  between  two  sticks  of  car- 
bon. The  tips  of  the  carbons  become  white  hot.  Edison,  after 
several  trials  along  other  lines,  thought  of  trying  a  thread  of 
carbon.  For  three  days  he  worked  without  sleep  to  prepare  a 
carbon  thread.  Finally  he  succeeded  in  sealing  a  good  carbon 
thread  made  from  cotton  into  a  glass  bulb.  He  pumped  the 
air  out  of  the  bulb  to  prevent  oxidation,  and  passed  a  current 


FIG.  135.  Thomas  A.  Edison. 


LIGHTING  OUR  HOMES  269 

through  the  fine  filament.  He  was  rewarded  by  a  light  that 
glowed  brilliantly. 

To  find  the  best  material  for  the  filaments,  he  sent  all  over  the 
world  and  spent  about  a  hundred  thousand  dollars.  The  result 
of  the  search  was  a  Japanese  bamboo  which  made  a  very  good  car- 
bon filament.  In  1880  the  first  commercial  electric  lighting  plant 
was  installed. 

"  A  great  invention  is  never  completed  by  one  man."  New  and 
better  filaments  have  been  devised.  For  the  pioneer  work  which 
resulted  in  giving  us  the  electric  lights  in  our  houses,  however,  we 
must  thank  Thomas  A.  Edison. 

INDIVIDUAL  PROJECTS 

«T 

Working  projects: 

1.  Make  a  list  of  all  the  things  which  you  can  find  at  home  which  reflect  light. 
Arrange  them  in  order,  beginning  with  the  object  that  gives  the  clearest 
image,  and  ending  with  the  object  which  merely  diffuses  the  light. 

2.  Make  a  collection  of  pictures  taken  in  different  ways,  including  daguerre- 
otypes, tintypes,  old  and  modern  photographs.     Find  out  how  methods 
of  taking  pictures  have  been  improved. 

3.  Take  some  pictures,  develop  the  films  or  plates,  and  print  the  pictures. 

4.  Compare  the  cost  of  lighting  a  room  by  a  kerosene  lamp,  an  open  gas 
burner,  a  Welsbach  burner,  and  an  electric  light.   To  do  this  measure  the 
kerosene  in  the  lamp,  let  it  burn  one  hour,  and  measure  again.     Compute 
the  cost  of  the  oil.     Read  the  gas  meter,  light  the  gas  in  the  room  you  are 
testing,  but  in  no  other  room,  and  read  again  in  one  hour.    Measure  the 
electricity  used  in  a  similar  way,  by  meter.     Compute  the  cost  at  local 
rates. 

5.  Make  a  sun-dial. 

6.  Make  acetylene  gas.     Put  a  few  small  lumps  of  calcium  carbide  into  water 
in  a  large  test-tube  or  a  can.    Light  the  gas  which  bubbles  off.     (Caution!) 
Demonstrate  how  an  acetylene  bicycle  lamp  works. 

7.  Make  and  use  a  sal-ammoniac  cell.     You  will  need  a  glass  jar,  two  elec- 
trodes of  carbon  and  of  zinc,  and  a  solution  of  sal-ammoniac,  which  you 
can  buy  at  a  hardware  store.     After  you  have  put  your  cell  together,  use 
it  to  ring  an  electric  bell  or  light  a  light. 

Reports: 

Examine  the  list  of  books  on  page  270.  Will  you  choose  one  of  the  subjects 
mentioned  there  to  investigate?  Probably  you  have  thought  of  other  subjects, 
too.  Look  them  up  in  the  library,  or  find  out  in  some  other  way  what  you  need 
to  know.  A  few  more  suggestions  follow: 

How  a  pocket  flash-light  works. 

How  a  gas-meter  works. 

The  storage  battery  in  an  automobile. 

How  daguerreotypes  were  made. 


270     PROTECTION  —  HOMES  AND  CLOTHING 

BOOKS  THAT  WILL  HELP  YOU 

Benjamin  Franklin.     P.  E.  More.    Houghton  Mifflin  Co. 
The  Book  of  Wonders.     Presbrey  Syndicate,  New  York. 

Articles  on  a  periscope,  illuminating  gas,  and  moving  pictures. 
Great  Inventors  and  their  Inventions.     F.  P.  Bachman.     American  Book  Co., 

"Edison." 

How  to  make  Good  Pictures.    Eastman  Kodak  Co.,  Rochester,  New  York. 
The  Lens  Part  of  Photography.    Gray-Lloyd  Manufacturing  Co.,  Ridgewood, 

New  Jersey. 
Modern  Triumphs.     E.  M.  Tappan,  Editor.     Houghton  Mifflin  Co. 

"Edison  and  the  Electric  Light." 

Physics  of  the  Household.     C.  J.  Lynde.     The  Macmillan  Co. 
Safety  for  the  Household.     Circular  75,  U.S.  Bureau  of  Standards. 

May  be  obtained  free  through  Congressmen. 
Scientific  American  Supplement.     May  6,  1916. 

"Sunlight  a  Necessity  for  the  Maintenance  of  Health." 
Scientific  American,  August  5,  1916. 

"A  Periscope  that  enables  a  Towerman  to  see  around  a  Railroad  Bend." 
Something  to  Do,  Boys.     E.  A.  Foster.    W.  A.  Wilde  Co. 

How  to  make  a  sun-dial. 
Stories  of  Inventors.     R.  Doubleday.    Doubleday,  Page  &  Co. 

How  moving  pictures  came  to  be. 
Wonders  of  Science.    E.  M.  Tappan,  Editor.    Houghton  Mifflin  Co. 

"An  Interview  with  Edison." 

"Making  Moving  Pictures." 

"How  a  Volcano  painted  the  Sky." 


PROJECT  XIII 
HEATING  OUR  HOMES 

The  necessity  of  heat.  Those  of  us  who  live  in  a  so-called 
temperate  climate  know  that  at  times  we  must  have  some  way  of 
heating  our  homes.  In  your  project  on  air  and  fire  you  have 
found  that  wherever  oxidation  is  going  on,  heat  is  given  off. 
Man  has  invented  ways  of  using  the  heat  produced  by  oxidation 
to  give  him  warmth  and  comfort  in  his  home.  In  this  project  we 
shall  find  out  some  of  the  ways  of  heating  in  common  use,  and  the 
principles  on  which  they  depend. 

PROBLEM  i :  WHAT  FUELS  ARE  USED  TO  HEAT  THE  SCHOOLHOUSE? 

Directions: 

Go  to  the  furnace-room  of  the  school. 

What  fuel  is  used  in  the  furnace  ?  Do  you  know  where  it  comes  from, 
and  how  it  is  formed? 

Ask  the  fireman  to  open  the  furnace  doors  to  let  you  see  the  fire. 

What  is  the  color  of  the  flames?  What  is  the  substance  which  produces 
the  light? 

Where  does  the  smoke  go? 

What  is  left  after  the  fuel  is  burned? 

Summary: 

Sum  up  what  you  have  learned  about  the  way  heat  is  provided  in  your 
schoolhouse,  and  about  the  way  that  the  fuel  burns. 

PROBLEM  2 :  To  COMPARE  DIFFERENT  GRADES  OF  HARD  COAL. 

Directions: 

Procure  from  a  coal  dealer  a  specimen  of  each  kind  of  coal  he  sells,  such 
as  pea,  nut,  stove,  egg,  and  furnace  coal. 

What  is  the  difference  between  them? 

Find  out  the  prices  of  each  kind,  when  sold  by  the  ton,  half  ton,  quarter 
ton,  and  bag. 

Summary: 

What  is  the  most  economical  way  of  buying  coal? 


272     PROTECTION  —  HOMES  AND  CLOTHING 


PROBLEM  3 :  To  MAKE  COKE. 

Directions: 

Grind  some  soft  coal  and  put  it  in  a  test-tube  fitted  with  a  bent  glass 
tubing  drawn  out  to  a  jet.     (See  diagram.)     Weigh  the  test-tube. 

Heat  the  test-tube  over  a 
Bunsen  burner. 

What  appears  in  the  side 
of  the  tube? 

What  comes  out  of  the  end 
of  the  tube?  Will  it  burn? 

What  is  the  appearance  of 
the  coke  left  in  the  tube?  Is 
it  lighter  or  heavier  than  the 
soft  coal  we  started  with? 
Compare  the  space  occupied 
by  the  coke  and  the  soft 
coal. 


FIG.  136.  Making  coke  in  the  laboratory. 


Summary: 

Name  three  substances  pro- 
duced by  burning  soft  coal. 
Question: 

Can  you  put  a  ton  of  coke  in  a  bin  which  is  just  large  enough  to  hold  a 
ton  of  coal?  Explain. 

PROBLEM  4:  WHAT  ARE  THE  PARTS  OF  A  COAL  RANGE? 

Directions: 

Procure  a  stove  catalogue.  With  the  aid  of  the  catalogue  study  the 
parts  of  the  coal  range  at  home. 

Diagram: 

Make  a  careful  diagram  of  the  stove  at  home.  Label  all  the  important 
parts. 

Question: 
Can  you  burn  furnace  coal  in  your  kitchen  range?    Why? 

PROBLEM  5 :  To  BUILD  A  FIRE. 

Directions: 

Part  i.  To  build  a  fire  at  home. 

Ask  your  mother  to  allow  you  to  build  the  fire  in  the  kitchen  stove. 
What  materials  do  you  use?  In  what  order  do  they  burn?  Do  you  have 
any  difficulty  in  making  the  fire  burn? 

Part  2.  To  build  a  fire  at  school. 

Let  one  member  of  the  class  build  a  fire  in  an  old  pan  at  school. 


HEATING  OUR  HOMES  273 

What  materials  are  used?      In  what  order  do  they  burn? 
Does  the  coal  kindle?     Try  pieces  of  different  sizes.     Can  you  make 
any  of  them  kindle? 

Questions: 

1.  Why  must  more  than  one  kind  of  material  be  used  to  kindle  a  fire? 

2.  Is  the  same  amount  of  heat  necessary  to  set  fire  to  one  piece  of  coal 
as  to  set  fire  to  a  shovelful  of  coal? 

3.  Which  size  of  hard  coal  is  easiest  to  kindle? 

PROBLEM  6:  How  DOES  THE  DRAFT  OF  A  STOVE  WORK? 

Directions: 

Light  a  joss  stick  and  hold  it  in  turn  in  front  of  all  the  openings  of  your 
coal  range.  Where  does  the  smoke  go? 

By  arrows  on  your  diagram  of  the  stove  show  the  direction  of  the  cur- 
rents of  air. 

Questions: 

1.  What  gas  in  the  air  is  useful  in  making  the*  fire  burn? 

2.  How  does  air  behave  when  heated? 

3.  Why  does  the  smoke  go  up  the  chimney? 

4.  How  can  you  make  the  fire  burn  faster? 

PROBLEM  7:  How  is  MY  HOUSE  HEATED? 

Directions: 

Examine  the  heating  system  at  home. 

1.  What  is  the  source  of  heat? 

2.  Where  is  the  heater  located? 

3.  How  is  the  heat  distributed  to  the  rooms? 

4.  Does  the  heating  system  furnish  fresh  air  with  the  heat?    If  so,  how? 

5.  If  you  wish  to  get  more  heat,  what  must  you  do? 

6.  If  you  wish  to  get  less  heat,  what  must  you  do? 

7.  Are  there  any  disadvantages  in  the  method  of  heating?  —  If  so,  what 
are  they? 

Diagram: 

Make  a  careful  diagram  of  the  heating  system  at  home.  Label  its  im- 
portant parts. 

PROBLEM  8 :  To  STUDY  A  STEAM  BOILER. 

Directions: 

Inspect  the  boilers  in  the  engine-room  of  the  school,  in  an  apartment 
house,  or  at  home. 

1.  Where  does  the  water  enter  from  the  city  pipes? 

2.  How  is  the  water  heated  to  steam? 


274    PROTECTION --HOMES  AND  CLOTHING 

3.  Find  the  water  gauge.     Make  a  sketch  of  it.     What  is  its  purpose? 
Its  importance? 

4.  Find  the  pressure  gauge.     Make  a  sketch  of  it.    What  is  its  purpose? 

5.  Find  the  safety  valve.     Explain  how  it  works.     What  is  its  impor- 
tance? 

Questions: 

1.  What  work  is  done  by  the  steam  generated  in  these  boilers? 

2.  What  three  safety  devices  are  attached  to  the  boiler? 

PROBLEM  9:  How  is  THE  SCHOOL  HEATED  AND  VENTILATED? 

Directions: 

1.  Visit  the  furnace-room  of  the  school.    Is  the  school  heated  by  steam, 
hot  water,  or  hot  air? 

2.  How  is  the  heat  distributed  to  the  rooms? 

3.  How  is  fresh  air  admitted  to  the  rooms? 

4.  Does  heated  air  enter  the  rooms  or  is  the  air  heated  after  it  enters? 

5.  How  is  the  impure  air  removed  from  the  rooms? 

Summary: 

Write  an  account  in  your  notebook  about  the  school  heating  and  venti- 
lating system,  illustrating  with  diagrams. 

PROBLEM  10:  To  STUDY  A  GAS  STOVE. 

Directions: 

Part  I.  A  Bunsen  burner. 

Light  a  Bunsen  burner.  What  are  the  results  when  you  allow  no  air  to 
enter  at  the  base? 

Slowly  turn  the  base  to  allow  more  air  to  enter.    What  are  the  results? 

Adjust  the  burner  to  produce  a  noiseless  blue  flame. 

Part  2.  A  gas  stove. 

Examine  a  gas  stove  carefully.  Find  the  pipes  which  admit  gas.  Find 
the  air  regulator  at  the  front  of  each  burner. 

Shut  off  the'  air-supply  from  one  burner.  Explain  the  effect  on  the 
flame. 

Find  how  to  adjust  the  air  regulator  to  produce  a  noiseless  blue  flame. 

Questions: 

1.  What  causes  the  gas  to  burn  with  a  yellow  flame? 

2.  What  kind  of  flame  gives  most  heat? 

PROBLEM  1 1 :  WHAT  is  THE  MOST  ECONOMICAL  WAY  OF  COOKING  WITH  GAS? 

Directions: 

Fill  two  kettles  of  the  same  size  three-fourths  full  of  water.  Place  them 
on  two  burners  of  a  gas  stove,  and  light  the  gas.  Peel  some  potatoes  and 


HEATING  OUR  HOMES  275 

cut  them  into  inch  cubes.  Then  drop  the  same  number  of  cubes  into  each 
kettle.  When  the  water  in  both  kettles  begins  to  boil,  turn  down  the  gas- 
flame  under  one  kettle  so  that  the  water  boils  slowly,  and  turn  up  the  gas- 
flame  under  the  other  kettle  so  that  the  water  boils  rapidly. 

Which  potatoes  do  you  expect  will  be  cooked  first? 

Test  the  potatoes  with  a  fork  every  few  minutes  until  they  are  done. 
Keep  a  record  of  the  time  required  for  each  lot. 

With  a  thermometer  find  the  temperature  of  the  boiling  water  in  each 
kettle. 

In  which  kettle  is  more  water  evaporated? 

What  two  things  are  accomplished  by  the  heat? 

Which  kettle  uses  more  gas? 

Conclusion: 
What  have  you  learned  about  economy  in  boiling  food  over  a  gas-flame? 

Fuel.  When  we  warm  our  houses  in  the  winter  we  are  obliged 
to  use  heat  which  we  obtain  by  burning  some  kind  of  fuel.  The 
common  fuels  are  wood,  coal,  coke,  petroleum,  gasoline,  kerosene, 
natural  gas,  and  illuminating  gas. 

Wood  as  a  fuel.  As  a  rule,  the  softer  woods  burn  more  readily 
than  the  hardwoods.  We  may  use  wood  merely  for  kindling  a 
fire ;  in  that  case  we  wish  a  wood  which  will  catch  fire  quickly  and 
give  off  a  large  amount  of  heat,  and  we  select  a  softwood.  If  we 
wish  a  wood  which  will  burn  a  long  time  and  make  good  " coals," 
we  select  a  hardwood.  The  heating  value  of  a  cord  of  heavy 
hardwood  is  practically  equal  to  the  heating  value  of  a  ton  of  coal. 
A  cord  of  lighter  wood,  like  cedar,  poplar,  spruce,  or  pine,  gives 
off  about  the  same  amount  of  heat  as  half  a  ton  of  coal. 

The  story  of  coal.  From  wood  to  coal  seems  a  long  step,  yet 
coal  is  transformed  wood.  The  greatest  coal-fields  of  the  United 
States  are  in  Pennsylvania.  Geologists,  scientists  who  study  the 
history  of  the  earth,  say  that  in  ages  past  the  land  was  low  and 
swampy.  The  climate  was  much  warmer  than  it  is  now,  and  the 
air  contained  larger  quantities  of  carbon  dioxide  and  water. 
Plants  were  able  to  use  the  carbon  dioxide  from  the  air  and  water 
from  the  swamps  to  make  food  rapidly  (see  page  157),  and  there- 
fore grew  to  be  of  great  size.  Fossil  ferns  have  been  found 
which  must  have  grown  thirty  feet  high.  As  the  dense  growth 
of  the  swamp  died,  it  fell  into  the  water.  There  it  could  not  easily 


276    PROTECTION  —  HOMES  AND  CLOTHING 

decay  because  of  lack  of  oxygen.  (See  page  241.)  As  more  and 
more  accumulated,  it  turned  into  a  solid  mass  similar  to  the  peat 
which  we  find  in  many  swamps  to-day. 

As  more  vegetation  grew  and  died,  the  layer  of  peat  became 
deeper.  The  pressure  of  the  topmost  layers  caused  the  lower 
layers  to  become  compact.  Great  quantities  of  the  brown  rock- 
like  coal  thus  formed  exist  in  the  earth's  crust  now.  It  is  called 
lignite,  and  is  not  very  good  for  fuel. 

Soft,  or  bituminous,  coal  was  made  when  the  pressure  was  enough 
to  drive  off  nearly  all  the  gas,  and  to  leave  mostly  carbon.  Soft 
coal  is  almost  82  per  cent  carbon. 

Hard,  or  anthracite,  coal  is  really  a  metamorphic  rock  made 
from  soft  coal  by  the  action  of  great  heat  and  pressure  in  the 
earth.  (See  page  127.)  It  is  94  per  cent  carbon.  Hard  coal  is 
a  much  cleaner  fuel  than  soft  coal  and  gives  off  less  gas,  smoke, 
and  tar  when  burning.  It  is  preferred  as  a  household  fuel  al- 
though its  kindling  temperature  is  much  higher  than  that  of  soft 
coal. 

How  to  build  a  fire.  In  your  study  of  air  and  fire,  you  have 
learned  that  a  match  can  be  lighted  because  enough  heat  has 
been  generated  in  the  head  of  the  match  to  raise  the  temperature 
of  the  wood  to  kindling  point.  We  must  apply  the  same  princi- 
ple, when  we  want  a  fire.  The  substance  to  be  burned  must  be 
raised  to  the  kindling  point  before  it  will  catch  fire.  When  we 
want  to  burn  hard  coal,  materials  of  lower  kindling  temperature 
must  first  be  set  on  fire  to  generate  enough  heat  to  raise  the  tem- 
perature of  hard  coal  to  the  kindling  point.  For  the  sake  of 
convenience  we  usually  use  paper  and  then  soft  wood  or  "  kind- 
ling" until  there  is  enough  heat  to  set  fire  to  the  coal. 

We  must  not  only  have  a  temperature  high  enough  to  kindle 
the  coal;  we  must  have  enough  heat  to  cause  a  "body"  of  coals 
to  burn. 

The  best  temperature  for  houses.  There  is  a  great  difference 
of  opinion  among  people  as  to  just  what  is  the  most  desirable 
temperature  for  a  room  to  have.  Some  people  seem  to  be  most 
comfortable  when  the  thermometer  registers  70°  F.  Others  like 
it  better  if  it  only  registers  65°  F.  It  is  impossible  to  set  any 


HEATING  OUR  HOMES 


277 


fixed  temperature  as  being  most  desirable  for  all  people.  It  is 
generally  true,  however,  that  between  65°  and  70°  is  most  health- 
ful. A  fluctuating  temperature  within  this  range  is  better  than 
a  constant  unchanging  temperature.  Many  people  make  them- 
selves more  susceptible  to  catching  cold  because  they  insist  upon 
having  their  homes  too  warm  during  the  winter. 

The  fireplace  as  a  heater.  We  enjoy  open  fireplaces  in  our 
living-rooms.  The  cheery  blaze  and  the  dancing  lights  and  shad- 
ows make  the  hearth  the 
center  of  a  home.  Yet 
if  we  were  obliged  to 
heat  our  homes  entirely 
by  fireplaces  we  should 
find  them  uncomfortable 
enough.  Near  the  fire 
the  room  is  too  hot  for 
comfort,  while  a  little 
distance  away  the  tem- 
perature may  be  below 
the  freezing  point. 

Three  ways  of  distribu- 
ting heat.  The  reason 
why  a  fireplace  is  a  poor  heater  for  a  room  is  that  it  fails  to  dis- 
tribute the  heat  all  through  the  room.  Heat  may  be  distributed 
in  three  ways,  by  radiation,  conduction,  and  convection. 

Radiation.  When  heat  is  distributed  by  radiation,  the  rays  travel 
through  space,  away  from  the  heat- giving  surface. 

We  know  that  the  energy  from  the  sun  is  sent  out  in  every 
direction.  The  sun's  rays  travel  through  space,  not  only  to  the 
earth,  but  to  all  other  parts  of  the  solar  system,  and  even  beyond. 
(See  page  217.)  We  receive  our  heat  by  radiation  from  the  sun. 

Nothing  is  heated  by  radiant  energy  from  the  sun  unless  it 
absorbs  some  of  the  waves.  Scientists  have  estimated  that  the 
temperature  of  space  between  the  earth  and  the  sun,  beyond 
the  zone  of  the  earth's  atmosphere,  is  459°  F.  below  zero.  If  the 
waves  are  absorbed,  the  object  becomes  hot  and  gives  off  some 
of  its  heat  to  the  air  around  it,  in  every  direction.  We  say  that 


FIG.  137.  Currents  of  air  in  a  room  heated  by  a 
fireplace. 


278     PROTECTION  —  HOMES  AND  CLOTHING 

it  radiates  heat.  Anything  which  absorbs  heat  quickly  also  ra- 
diates heat  quickly. 

The  darker  an  object  is,  the  more  it  absorbs  heat.  Soil  heats 
more  quickly  than  water,  and  gives  off  its  heat  by  radiation  more 
quickly.  A  black  stove  radiates  more  heat  than  it  would  if  it 
were  nickel-plated  all  over.  A  black  kettle  cools  more  quickly 
than  an  aluminum  kettle  because  it  radiates  more  quickly.  A 
radiator  gives  off  more  heat  by  radiation  if  it  is  black  or  bronze 
than  if  it  is  painted  a  light  color.  In  the  case  of  a  radiator,  how- 
ever, heat  is  given  off  in  other  ways;  only  about  40  per  cent  of  all 
the  heat  given  off  by  a  radiator  is  distributed  by  radiation. 

Conduction.  When  heat  is  transferred  from  one  particle  to  an- 
other, the  process  is  called  "conduction" 

A  silver  spoon  in  a  cup  of  hot  coffee  may  become  hot  to  the 
end  of  the  handle.  The  bowl  of  the  spoon  in  the  coffee  becomes 
hot;  it  heats  the  particles  farther  up  the  handle,  and  so  on  to  the 
end.  When  you  touch  the  spoon,  the  heat  is  passed  on  to  your 
skin  by  conduction.  In  order  that  heat  may  be  conducted  from 
one  object  to  another,  the  two  objects  must  be  in  contact,  or 
touching  each  other. 

Some  substances  are  much  better  conductors  of  heat  than  others. 
Silver  is  the  best  known  conductor,  and  air  is  one  of  the  poorest. 
The  metals  are  all  good  conductors.  Study  the  table  to  see  the 
best  conductors,  the  medium  conductors,  and  the  poor  conductors. 
Can  you  see  why  certain  substances  are  preferred  for  building 
houses  and  others  for  use  in  stoves  and  heaters? 


Good  conductors 

Medium  conductors 

Poor  conductors 

Silver 

Granite 

Wood 

Copper 

Limestone 

Asbestos  paper 

Aluminum 

Ice 

Sawdust 

Brass 

Brick 

Paper 

Zinc 

Glass 

Linen 

Tin 

Water 

Cotton 

Iron 

Plaster 

Silk 

Wool 

Air 

Convection.     The  third  method  of  transferring  heat  is  called 
convection.    You  are  familiar  with  it  if  you  have  studied  the 


HEATING  OUR  HOMES 


279 


project  on  water  in  the  air.    (See  page  1 1 1 .)     You  know  that  one 
great   cause  for  winds 
is     the     formation    of 

currents. 

distributed 


OCOOT' 


convection 

When  heat  i 

by  convection,  the  heated 

particles  themselves  move, 

forming  a  current.  Con- 
vection    currents     are 

formed  in  gases  like  air, 

and  in  liquids  like  water. 

We  shall  find  that  we 

depend  upon  convection 

more  than  on  either  of 

the  other  two  processes 

in  heating  our  homes. 
The  stove  as  a  heater.    The  first  stoves  were  made  nearly  fifty 

years  before  the  Revolutionary  War.   They  were  at  first  just  iron 

boxes  with  a  door  at  one 
end  and  an  opening  in  the 
top  to  let  out  the  smoke. 
Then  one  of  our  greatest 
American  scientists,  Ben- 
jamin Franklin,  invented 


FIG.  138.  A  kitchen  stove.    Study  the  drafts,  as  shown 
by  arrows. 


IT 


"-»   s 


FIG.  139.  A  jacketed  stove.  A  metal  jacket 
around  the  stove  improves  its  value  as  a  heater. 
Convection  currents  are  started  when  the  cold  air 
presses  in  at  the  bottom  of  the  jacket  and  forces  the 
lighter  heated  air  up, 


the  "  Pennsylvania  Fire- 
place," which  is  still  in 
use  in  some  places  and 
known  as  a  "  Franklin 
Stove."  It  was  really  a 
small  open  fireplace  of 
iron  to  be  placed  inside 
the  old  fireplace  and  ex- 
tend partly  out  into  the 
room.  The  advantages 
over  the  old  fireplace  were 
that  the  iron  became  hot 
and  radiated  heat  into 


280    PROTECTION  —  HOMES  AND  CLOTHING 


the  room  better  than  the  brick.  It  also  conducted  heat  to  the 
layer  of  air  next  to  it,  so  that  convection  currents  were  started 
in  the  room  with  the  result  that  not  so  much  of  the  heat  es- 
caped up  the  chimney. 

An  important  part  of  a  stove  is  the  draft  which  admits  air 
to  furnish  oxygen  enough  to  burn  the  fuel.  The  amount  of  air 
which  enters  may  be  regulated  by  means  of  dampers.  Every  one 
should  know  how  to  regulate  the  draft  of  a  stove  to  get  the 
most  heat  from  the  smallest  amount  of  fuel.  Remember  that  as 
any  fuel  burns  gases  are  given  off,  which  in  their  turn  burn  and 
give  heat. 

A  hot-air  furnace.  The  usual  furnace  for  heating  a  house  by 
heated  air  is  really  a  jacketed  stove  situated  in  the  basement  and 

supplied  with  pipes  which  can 
distribute  the  hot  air  all  over 
the  house.  It  is  the  cheapest 
heating  system  to  install,  and 
is  very  satisfactory  in  small 
houses,  if  the  following  prin- 
ciples are  followed: 

The  air  should  be  abundant. 
The  volume  of  heated  air 
which  enters  the  room  should 
be  large,  so  that  a  constant 
supply  of  fresh  heated  air  may 
be  obtained.  Fresh  air  will 
not  enter  unless  some  means  is 
given  for  the  used  air  to  es- 
cape. A  small  quantity  of  air 

always  escapes  through  cracks  and  through  porous  walls.  A 
window  open  an  inch  or  two  at  the  top  allows  some  used  air 
to  escape  and  an  equal  quantity  of  warm  air  to  enter  from  the 
furnace  pipes,  unless  a  strong  wind  forces  air  into  the  room 
through  the  window. 

The  air  should  be  fresh.  Most  furnaces  admit  air  directly  from 
outside  through  a  cold  air  inlet.  The  air  becomes  heated  when 
in  contact  with  the  furnace  walls,  and  convection  currents  are 


FIG.  140.  A  hot-air  furnace.  Fresh  air  enters 
the  outer  jacket  of  the  furnace  at  A,  is  heated 
and  passes  out  the  pipes  C  to  the  rooms.  The 
flue  B  allows  the  gases  from  the  fire  to  escape 
into  the  chimney. 


HEATING  OUR  HOMES 


281 


started  which  carry  the  heated  fresh  air  to  every  room  in  the 
house.  A  furnace  which  uses  only  the  air  of  the  basement  is  un- 
satisfactory since  it  does  not  furnish  enough  fresh  air. 

The  air  should  be  moistened.  As  air  is  heated,  its  ability  to  hold 
water  vapor  increases.  (See  page  108.)  The  air  may  thus  be- 
come too  dry.  Furnaces  are  usually  provided  with  a  water  pan, 
which  should  be  kept  full  of  water.  Dryness  is  felt  more  keenly 
in  temperatures  above  68°. 


FIG.  141.  A  hot-water  heating  system.  Trace  the  movement  of  the  water  through  the  pipes 

and  radiators. 

Hot-water  heating.  When  houses  are  heated  with  hot  water, 
convection  currents  are  used,  just  as  in  the  hot-air  system,  but 
the  currents  are  produced  in  water  rather  than  in  air. 

The  water  heater  is  usually  placed  in  the  basement.  The  hot 
water  flows  from  the  top  of  the  heater  through  main  flow  pipes, 
to  radiators  in  the  rooms.  The  water  cools  as  it  circulates  through 
the  radiators  and  returns  to  the  bottom  of  the  heater  through 
return  flow  pipes.  The  water  is  used  over  and  over  again. 

The  rooms  are  heated  both  by  radiation  from  the  heated  sur- 
face of  the  radiators,  and  by  convection  currents,  which  are  started 
as  soon  as  the  layer  of  air  in  contact  with  the  radiator  becomes 
warm. 


282     PROTECTION --HOMES  AND  CLOTHING 

You  notice  that  the  hot-water  system  provides  no  way  of 
keeping  the  air  in  the  room  fresh.  This  is  sometimes  accom- 
plished by  having  entrances  for  air  behind  the  radiators,  so  that 
the  air  is  heated  as  it  enters  and  passes  out  into  the  room.  If  no 
such  system  is  provided,  'the  windows  should  be  used  as  ventila- 
tors. The  air  should  be  kept  moist  by  allowing  water  to  evapo- 
rate. Dishes  of  water  are  often  kept  on  radiators.  A  more  beau- 
tiful way  is  to  keep  a  growing  plant,  like  a  fern,  in  the  room. 
Enough  water  evaporates  from  the  leaves  of  a  large  fern  to  keep 
the  air  of  a  living-room  comfortably  moist. 

Since  water  expands  when  heated  (see  page  74)  an  expansion 
tank  must  be  provided.  It  is  usually  located  on  the  upper  floor. 
It  must  be  kept  from  freezing,  or  an  explosion  may  result.  Why? 

Steam  heat.  Although  the  parts  of  a  steam  heating  system 
look  very  much  like  the  parts  of  a  hot-water  system,  the  prin- 
ciples are  quite  different.  In  the  basement  is  the  heater,  or 
boiler,  where  a  fire  changes  water  to  steam.  Instead  of  being 
full  of  water,  as  is  the  case  with  the  hot-water  heater,  the  steam 
boiler  is  only  partly  full.  The  water  is  heated  to  the  boiling 
point  and  changes  to  steam.  The  upper  part  of  the  boiler  is 
therefore  full  of  steam.  As  more  water  changes  to  steam,  the 
steam  pressure  increases.  Every  boiler  is  supplied  with  a  pres- 
sure gauge.  If  the  pressure  becomes  too  great  for  safety,  some  of 
the  steam  escapes  through  the  safety  valve.  The  amount  of  water 
in  the  boiler  can  be  seen  by  looking  at  the  water  gauge. 

Steam  is  forced  by  steam  pressure  up  into  the  steam  pipes  and 
radiators,  which  are  fitted  with  valves  to  control  the  entrance  of 
the  steam.  In  the  radiator,  steam  is  condensed  to  water.  Ex- 
actly as  much  heat  is  given  off  when  steam  condenses  as  was  put 
into  the  water  to  change  it  to  steam.  You  can  see,  therefore, 
that  the  reason  for  the  heat  in  the  radiator  is  very  different  from 
the  reason  for  the  heat  in  a  hot-water  radiator.  The  room  is 
heated,  however,  in  exactly  the  same  way,  partly  by  radiation, 
but  mostly  by  convection  currents. 

The  condensed  water  occupies  much  less  space  than  the  steam, 
and  therefore  more  steam  constantly  enters,  as  long  as  the  valve 
is  open.  The  water  returns  to  the  boiler  to  be  heated  over  again. 


HEATING  OUR  HOMES 


283 


As  with  the  hot-water  system,  the  steam  heating  system  pro- 
vides no  means  of  procuring  enough  fresh  air  and  moisture. 
Each  householder  should  be  sure  that  his  house  is  well  ventilated. 


FIG.  142.     A  steam  heating  system.     Trace  the  course  of  the  steam  to  the 
radiators,  and  the  way  the  water  returns  to  the  boiler. 

Steam  is  the  best  system  to  use  in  heating  large  buildings,  since 
hot  water  and  hot  air  cannot  be  successfully  carried  long  dis- 
tances. Many  buildings  can  be  heated  from  one  central  heating 
plant  when  steam  is  used.  Such  systems  are  used  on  college 
campuses,  and  even  in  sections  of  some  cities. 

Gas  heaters.  Other  fuels  besides  wood  and  coal  are  fre- 
quently used.  In  certain  sections  of  the  country  natural  gas 
issues  from  the  earth  in  such  abundance  as  to  be  piped  to  houses 
for  use  in  heaters  and  in  cooking-stoves.  Illuminating  gas  is 
commonly  used  for  cooking  purposes  and  sometimes  for  heating 
purposes.  The  flame  used  is  the  colorless  blue  flame  which  is 
much  hotter  than  the  yellow  flame,  since  oxidation  is  so  much 
more  rapid.  If  you  have  tried  problem  II  on  page  274,  you  have 
perhaps  been  surprised  to  learn  that  after  a  liquid  begins  to  boil, 
food  cooks  just  as  rapidly  when  the  flame  is  turned  low  enough  to 


284     PROTECTION --HOMES  AND  CLOTHING 

allow  a  gentle  boiling,  as  it  does  when  boiling  violently  over  a  high 
flame.  Every  one  who  uses  a  gas  stove  should  realize  and  make 
use  of  this  fact,  in  order  to  use  gas  economically. 


INDIVIDUAL  PROJECTS 


FIG.  143.  Longitudinal  section  through 
fireless  cooker,  showing  details  of  the  con- 
struction: A,  outside  container  (wooden 
box,  old  trunk,  etc.);  B,  packing  or  in- 
sulating material  (crumpled  paper,  cin- 
ders, etc.);  C,  metal  lining  in  nest;  D, 
cooking  kettle;  E,  soaps  tone  plate,  or 
other  source  of  heat;  F,  pad  of  excelsior 
for  covering  top;  G,  hinged  cover  of  out- 
side container. 

(Courtesy,  U.S.  Dept.  Agriculture.) 


Working  projects: 

1.  Make  a  fireless  cooker. 

Directions  may  be  found  in  Farmers' 
Bulletin  771,  U.S.  Department  of  Agri- 
culture. 

2.  Make  a  model  of  a  hot-water  heating 
system. 

Use  glass  tubing  for  pipes  and  radia- 
tor, a  flask  and  Bunsen  burner  for  the 
heater,  and  a  funnel  tube  for  the  expan- 
sion tank.  Place  colored  water  in  the 
flask,  and  see  that  all  connections  are 
very  tight.  Demonstrate  to  the  class 
how  the  heating  system  works. 

3.  Demonstrate  the  principle  of  a  ther- 
mos bottle. 

Send  to  firms  which  make  them  for 
catalogues,  and  study  the  structure. 
By  means  of  a  bottle  which  can  be 
unscrewed  and  diagrams  on  the  board, 
explain  the  principle. 

4.  Take   care  of  the   heating  system  in 
your  house  for  a  month. 

5.  Build  the  kitchen  fire  every  day  for  a 
month. 


FIG.  144.  Two  electric  cooking  devices.  Wires  are 
heated  red-hot  by  their  resistance  to  the  electric  cur- 
rent. 

(Courtesy,  Edison  Electric  Appliance  Co.) 


FIG.  145.  An  electric  heater. 
Resistance  to  the  electric  cur- 
rent produces  heat  which  is  sent 
out  into  the  room  by  the  curved 
metal  surface. 

(Courtesy,  Edison  Electric 
Appliance  Co.) 


HEATING  OUR  HOMES  285 

6.  If  your  house  is  heated  by  steam  or  hot  water,  make  humidifiers  for  the 
rooms.  One  way  is  to  fasten  a  can  by  wire  behind  the  radiator.  Keep  it 
constantly  filled  with  water. 

Reports: 

1.  Procure  a  coal  weigher's  certificate  and  explain  to  the  class  just  how  it 
protects  a  purchaser  of  coal. 

2.  The  development  of  the  stove. 

See  Burns's  Story  of  Great  Inventions. 

3.  Natural  gas. 

Find  out  the  sections  of  the  country  where  it  may  be  obtained,  how  it  is 
piped  to  houses,  and  how  used  as  a  fuel. 

4.  Cooking  by  electricity. 

5.  Heating  by  electricity. 

6.  Peat  as  a  fuel. 

7.  Moisture  and  heating  systems. 

8.  The  work  of  an  electric  furnace. 

BOOKS  THAT  WILL  HELP  YOU 

Electricity  and  its  Every-Day  Uses.     J.  F.  Woodhull.    Doubleday,  Page  &  Co. 
Fireless  Cooker. 

Farmers'  Bulletin  771,  U.S.  Department  of  Agriculture. 
Household  Physics.     A.  M.  Butler.    Whitcomb  and  Barrows.     Boston,  1915. 
Humidity  and  its  Effect  on  our  Health  and  Comfort.     P.  R.  Jameson.     Taylor 

Instrument  Cos.,  Rochester,  New  York. 

The  Humidostat.     Johnson  Service  Co.,  35  Hartford  St.,  Boston. 
Measurements  for  the  Household. 

Circular  55,  Bureau  of  Standards,  Washington. 

The  Story  of  Great  Inventions.     E.  E.  Burns.     Harper  &  Bros.,  New  York, 
1912. 

Includes  the  electric  furnace. 

Scientific  American  Supplement.     Among  many  good  articles  may  be  men- 
tioned: 

"Electric  Cooking  Ranges  in  Hospitals."     April  29,  1916. 

"Gasolene  from  Natural  Gas."     March  18,  1916. 

"The  Utilization  of  Peat."     April  8,  1916. 

"The  World's  Largest  Electric  Kitchen."     March  18,  1916. 
Shelter  and  Clothing.     Kinne  and  Cooley.    The  Macmillan  Co.,  1914. 


PROJECT  XIV 
CLOTHING  AND  ITS  CARE 

Where  our  clothes  come  from.  Have  you  ever  considered  how 
much  you  are  indebted  to  the  rest  of  the  world  for  the  cloth- 
ing that  you  wear  every  day?  The  leather  in  your  shoes  may 
have  been  made  from  hides  which  came  from  India  or  China. 
The  cotton  in  your  blouses  may  have  been  raised  in  our  own 
South  or  it  may  have  come  from  Egypt  or  India.  The  wool  in 
your  suit  perhaps  grew  on  sheep  which  grazed  in  Australia  or 
in  Argentina.  The  silk  in  your  hair  ribbons  or  neckties  may 
have  been  made  in  France,  in  China,  or  in  Japan.  Your  hand- 
kerchief is  made  of  linen  that  came  from  Ireland  or  from  Russia. 
Laborers  of  many  lands  toiled  to  produce  the  raw  materials; 
ships  and  railroads  transported  them  to  factories,  and  there  they 
were  made  into  clothing. 

The  science  of  clothing.  As  a  matter  of  course  you  wear  dif- 
ferent kinds  of  clothing  under  different  conditions,  dependent 
upon  the  weather  and  the  seasons.  To  find  the  real  scientific 
reasons  behind  your  choice,  solve  problems  1-5.  You  will  be  in- 
terested in  learning  why  certain  materials  are  suitable  for  use  in 
clothing,  while  others  are  not.  Problems  6-8  will  show  you  the 
reasons.  To  care  successfully  for  your  own  clothing  also  requires 
scientific  knowledge.  Laundering,  dyeing,  and  removing  stains 
are  all  chemical  processes.  Perform  problems  9-14  to  learn  the 
chemistry  of  these  operations. 

Many  of  the  other  special  sciences  contribute  to  our  scientific 
knowledge  of  clothing.  From  botany  we  learn  the  part  the  plant 
world  plays  in  furnishing  us  cotton,  flax,  and  other  plant  fibers. 
From  zoology  we  learn  the  part  played  by  animals,  such  as  the 
sheep,  and  the  silk  worm,  as  well  as  the  destructive  work  of  the 
clothes  moth.  Physics  shows  us  the  relation  to  clothing  of  heat 
conduction,  of  evaporation,  of  water  absorption,  and  of  color. 

Many  individual  projects  will  suggest  themselves  to  you.    On 


CLOTHING  AND  ITS  CARE 


287 


the  subject  of  clothes,  much  has  been  written  on  which  to  base 
reports.  Exhibits  in  museums  may  be  found.  A  small  group  of 
pupils  might  well  make  a  preliminary  study,  and  later  show  the 
exhibit  to  the  whole  class.  Examine  the  suggestions  at  the  end 
of  this  chapter,  and  start  at  once  to  work  out  your  project. 

PROBLEM  i :  WHAT  is  THE  SCIENTIFIC  REASON  FOR  WEARING  DIFFERENT 
CLOTHING  IN  WINTER  AND  SUMMER? 

Directions: 

Find  the  temperature  of  your  body.     (See  problem  2  on  page  35.) 
From  charts  or  maps  find  the  average  temperature  of  your  locality  for 

January  and  for  July. 


FIG.  146.     Temperatures  in  the  United  States  in  January. 

Should  the  purpose  of  our  clothing  be  to  conduct  the  heat  away  from  the 
body  or  to  keep  it  near  the  body  in  January?  in  July? 

Questions: 

1.  When  should  clothes  be  made  of  materials  which  are  good  heat 
conductors?    Why? 

2.  When  should  clothes  be  made  of  materials  which  are  poor  heat  con- 
ductors?   Why? 

PROBLEM  2 :  How  DO  MATERIALS  USED  IN  CLOTHING  VARY  AS  CONDUCTORS 

OF  HEAT? 
Directions: 

Procure  pieces  of  different  materials  used  in  clothing*  such  as  cotton, 


288     PROTECTION  —  HOMES  AND  CLOTHING 

linen,  wool,  cotton  and  wool  mixture,  cotton  and  linen  mixture,  leather, 
etc. ;  also  newspaper. 

Fold  each  piece  to  make  a  pad  one  inch  thick.     Place  one  of  the  pads  on 
a  heated  surface. 


FIG.  147.    Temperatures  in  the  United  States  in  July. 

Place  a  thermometer  on  the  pad  with  the  bulb  touching  the  material. 
Watch  the  thermometer  for  four  minutes,  keeping  a  careful  record,  as 
follows: 


Material 

Tempera- 
ture at  first 

Tempera- 
ture after  i 
minute 

Tempera- 
ture after  2 
minutes 

Tempera- 
ture after  3 
minutes 

Tempera- 
ture after  4 
minutes 

Total 
change 

Try  each  material  separately,  bringing  the  mercury  back  to  the  same 
starting-place  each  time  by  dipping  the  thermometer  in  cold  water. 

Try  also  the  conductivity  of  air,  by  holding  the  bulb  of  the  thermometer 
one  inch  away  from  the  heater  at  the  side.  Why  would  the  results  be 
incorrect  if  the  bulb  were  held  above  the  heater? 


CLOTHING  AND  ITS  CARE  289 

Summary. 

1.  Name  the  materials  tested  in  the  order  of  their  ability  to  conduct 
heat,  starting  with  the  best  conductor. 

2.  What  is  the  value  of  layers  of  air  between  garments? 

Questions: 

1.  Why  does  kid  or  leather  make  a  good  vest? 

2.  Why  do  folded  newspapers  under  a  coat  add  "warmth"? 

PROBLEM  3:  WHY  DOES  THE  WIND  CHILL? 
Directions: 

Procure  two  thermometers. 

What  is  the  temperature  of  the  room? 

Support  the  two  thermometers  side  by  side.  Under  one  place  a  glass 
containing  water.  Wrap  the  bulb  of  the  thermometer  in  a  wick  of  absorb- 
ent cotton,  one  end  of  which  is  in  the  water  below.  The  water  should  be 
at  room  temperature.  What  happens  to  the  wick?  Why? 

Watch  the  two  thermometers,  taking  readings  every  minute.  Keep  the 
record  as  follows: 


In  still  air 

Dry  bulb  thermometer 

Wet  bulb  thermometer 

At  start 

After  i  minute 

2  minutes 

3  minutes 

4  minutes 

What  happens  to  the  water  that  reaches  the  top  of  the  wick?  How  is 
the  thermometer  affected? 

Now  try  fanning  the  air,  to  imitate  a  wind.     Keep  the  record  as  before. 
Account  for  any  differences. 
Conclusion: 

Why  do  you  feel  cooler  in  the  wind  than  in  still  air? 

Questions: 

1.  Why  does  fanning  oneself  usually  produce  a  cooling  effect? 

2.  Which  is  warmer  clothing  for  a  windy  winter  day,  two  wool  sweaters 
or  one  sweater  and  a  canvas  coat?    Why? 

PROBLEM  4 :  Do  DIFFERENTLY  COLORED  CLOTHS  VARY  IN  THEIR  ABSORP- 
TION OF  HEAT? 
Directions: 

Fasten  small  squares  of  cloth  of  different  colors,  including  white  and 
black,  around  the  bulbs  of  thermometers,  and  leave  them  in  the  sunlight, 
for  two  or  three  minutes. 

Do  they  absorb  equally  rapidly?     Account  for  any  differences. 


290     PROTECTION --HOMES  AND  CLOTHING 

Questions: 

1.  Why  does  the  color  of  clothing  affect  its  warmth? 

2.  Why  are  white  clothes  so  popular  in  summer? 

PROBLEM  5:  Do  MATERIALS  DIFFER  IN  THEIR  ABILITY  TO  RESIST  WATER? 

Directions: 

Cut  pieces  6X2  inches,  using  as  many  different  materials  as  possible, 
including  raincoat  or  cravenetted  cloth. 

Place  each  piece  in  a  glass  containing  one  inch  of  colored  water.  What 
causes  the  water  to  rise? 

By  means  of  a  rule  measure  each  minute  the  height  to  which  the  water 
has  risen. 

Keep  a  record  as  follows: 


Material 

Water  rises  in 
i  minute 

In  2  minutes 

In  3  minutes 

In  4  minutes 

Questions: 

1 .  Name  the  materials  tested  in  the  order  of  their  ability  to  resist  water, 
starting  with  the  most  waterproof  material.     How  does  the  ability  to 
resist  water  depend  on  the  kind  of  fiber  used? 

2.  How  does  the  coarseness  of  the  weave  affect  the  ability  to  resist 
water? 

3.  How  does  special  treatment,  as  in  raincoat  material,  affect  the  ability 
to  resist  water? 


PROBLEM  6:  How  DOES  THE  STRUCTURE  OF  THE  COTTON  FIBER  FIT  IT  FOR 
USE  IN  CLOTHING? 

Directions: 

Examine  a  cotton  boll.  What  part  of  the  plant  is  it?  What  does  it 
contain?  Of  what  use  to  the  plant  is  the  cotton  fiber? 

Examine  a  very  small  amount  of  cotton  fiber  with  a  compound  micro- 
scope. Of  how  many  cells  does  each  fiber  consist?  What  is  the  shape  of 
a  cell?  Make  a  careful  sketch  of  a  fiber,  showing  the  cell-wall  of  cellulose, 
and  if  possible  the  remains  of  the  protoplasm.  Are  the  fibers  straight  or 
twisted?  Why  are  they  well  suited  for  weaving? 


CLOTHING  AND  ITS  CARE 


291 


Conclusion: 

State  the  characteristics  of  cotton  fibers  which  make  them  suitable  for 
making  cloth. 

PROBLEM  7 :  WHY  is  WOOL  USED  FOR  CLOTHING? 
Directions: 

Examine  specimens  of  raw  wool,  which  may  be  obtained  from  wool 
manufacturers. 

Examine  a  few  fibers  of  wool  with  a  compound  microscope.     Compare 
the  fibers  with  cotton  fibers  in  respect  to  straightness  and  surface.     Sketch 
a  few  fibers.     Would  wool  or  cotton  fibers  mat  together  better?    Why? 
Conclusion: 

What  characteristics  of  wool  fiber  make  it  suitable  for  cloth-making? 

PROBLEM  8:  WHY  is  SILK  USED  FOR  CLOTHING? 
Directions: 

From  what  is  silk  made? 

Examine  a  few  silk  fibers  from  the  cocoon  with  a  compound  microscope. 
How  many  filaments  compose  one  fiber?  From  what  you  know  about  how 
the  worm  spins  the  silk  would  you  expect  this?  Is  silk  fiber  twisted  like 
cotton?  Is  it  serrated  or  jagged  like  wool?  How  can  you  distinguish  it 
from  the  other  fibers?  Make  a  sketch  to  show  its  appearance. 
Conclusion: 

What  characteristics  of  silk  fiber  make  it  suitable  for  making  cloth? 
Question: 

Of  what  use  is  the  silk  filament  to  the  silkworm? 

PROBLEM  9:  How  DO  CLOTH  MATERIALS  VARY  IN  REGARD  TO  SHRINKAGE? 
Directions: 

Cut  samples  of  unshrunk  cotton,  wool,  linen,  and  silk  of  equal  size. 
Measure  width  and  length. 

Wash  the  samples  in  hot  water  and  soap.  When  dry,  measure  again. 
Keep  the  records  as  follows: 


BEFORE  WASHING 

AFTER  WASHING 

Length 

Width 

Area 

Length 

Width 

Area 

Cotton 
Wool 
Linen 
Silk 

Calculate  how  much  each  material  would  shrink  in  a  yard. 


292    PROTECTION  --  HOMES  AND  CLOTHING 

PROBLEM  10:  WHY  DOES  WASHING  WITH  SOAP  REMOVE  GREASE? 

Directions: 

Put  about  an  inch  of  water  in  a  test-tube.  Pour  a  little  oil  on  the  water. 
Do  the  liquids  mix?  Shake  the  tube  vigorously.  Describe  the  emulsion 
which  results.  Let  the  tube  stand  a  short  time.  Describe  the  results.  Is 
the  emulsion  permanent  or  temporary? 

Put  about  an  inch  of  soapy  water  in  a  test-tube.  Pour  in  a  little  oil.  Do 
the  liquids  mix?  Shake  the  tube  vigorously,  and  let  it  stand.  Is  the 
emulsion  permanent  or  temporary? 

Question: 

How  does  soap  act  on  grease? 

PROBLEM  1 1 :  To  REMOVE  STAINS  BY  SOLUTION. 

Directions: 

Consult  the  table  on  page  303. 

Stain  cloths  in  several  ways,  and  remove  the  stains  as  directed.  Bring 
the  samples  of  goods  to  school  to  show  the  stained  condition  and  the  con- 
dition after  stains  were  removed. 


PROBLEM  12:  To  REMOVE  STAINS  BY  ABSORPTION. 

Directions: 

Consult  the  table  on  page  303. 

Stain  cloths  with  greases  of  different  kinds  and  remove  the  stains  as 
directed. 

Bring  the  results  of  your  experiment  to  school  to  exhibit  to  the  class. 

PROBLEM  13:  To  REMOVE  STAINS  BY  BLEACHING. 

Directions: 

A  good  bleaching  liquid  for  cotton  goods  is  Javelle  water.  Enough  for 
each  member  of  the  class  to  obtain  a  small  bottleful  can  be  made  as  follows: 

Dissolve  one  half  pound  chloride  of  lime  in  one  quart  of  cold  water. 
!    Dissolve  one  pound  of  sal  soda  in  one  quart  of  boiling  water.     Stir  the 
two  solutions  together  thoroughly,  and  let  the  mixture  stand  overnight. 
Pour  off  the  clear  liquid  and  bottle. 

Stain  cloths  of  cotton,  silk,  linen,  and  wool  with  ink,  dye,  or  mildew. 

Make  a  weak  solution  of  Javelle  water  by  adding  one  teaspoonful  to  one 
quart  of  water.  Soak  the  cloths  in  it,  rub  .the  stains,  and  wash  in  clear 
water. 

Conclusion: 
Bring  the  results  of  your  experiment  to  school  to  exhibit  to  the  class. 


CLOTHING  AND  ITS  CARE 


293 


PROBLEM  14:  To  REMOVE  STAINS  BY  NEUTRALIZATION. 
Directions: 

Part  i.  What  is  a  neutral  substance? 

Examine  bottle  containing  acids,  bases,  and  salts. 

With  the  end  of  a  glass  rod  put  a  drop  of  acid  on  a  piece  of  litmus  paper, 
which  is  colored  by  a  dye  from  a  tiny  plant.  What  is  the  effect  on  the 
litmus  paper? 

Put  a  drop  of  an  alkali  on  the  litmus  paper.     What  is  its  effect? 

Put  a  drop  of  water  on  the  litmus  paper.  Has  it  any  effect?  Water  is 
neutral,  that  is,  neither  an  acid  nor  an  alkali.  Most  salts  are  also  neutral. 

Part  2.  What  substances  are  acid  or  alkaline? 

Place  a  bit  of  the  substance  that  you  wish  to  test  on  a  piece  of  moist 
litmus  paper,  and  observe  the  colors.  Record  your  results  in  a  table  as 
follows : 


ACIDS 

ALKALIES 

NEUTRAL 

Part  3.  To  neutralize  stains. 

Stain  pieces  of  colored  cloth  with  some  of  the  acids  and  alkalies  that  you 
have  found. 

To  the  acid  spots  add  a  drop  of  ammonia.     What  are  the  results? 

To  the  alkali  spots  add  a  little  lemon  juice,  vinegar,  or  oxalic  acid. 
What  are  the  results?  Exhibit  your  results  to  the  class. 

Questions: 

1.  How  can  a  substance  be  neutralized? 

2.  What  spots  can  be  removed  by  neutralization? 

The  purpose  of  clothing.  In  the  previous  project  we  studied 
different  methods  of  regulating  the  temperature  of  our  homes. 
The  reason  we  heat  our  homes  is  to  make  us  more  comfortable. 
The  clothing  we  wear  ought  to  serve  the  same  purpose.  On  cold 
days  we  wear  "  warmer,"  heavier  clothing  than  on  warm  days. 
We  change  the  weight  and  kind  of  our  clothes  as  the  seasons  vary. 


294    PROTECTION  —  HOMES  AND  CLOTHING 

The  materials  of  which  our  clothing  is  made  are  quite  different, 
in  character  and  texture.  Some  materials  are  better  for  summer ; 
others  are  more  suitable  for  winter. 

An  envelope  of  air  around  our  bodies.  The  usual  temperature 
of  the  human  body  is  98.6°  F.  (See  page  40.)  This  is  true  whether 
we  live  in  a  warm  climate  or  in  a  cold  climate.  The  cause  for  this 
comparatively  high  temperature  is  oxidation.  (See  page  30.) 
The  air  in  contact  with  the  body  becomes  warmed  to  nearly  the 
body  temperature.  Our  problem  in  cold  weather  is  to  keep  the 
body  heat  from  escaping,  and  in  warmer  weather  to  hasten  the 
escape  of  the  body  heat.  Therefore  we  wear  clothing  of  different 
materials. 

Clothes  as  conductors  of  heat.  Consult  the  table  on  page  278. 
You  notice  that  all  the  materials  of  which  clothes  are  made  are 
in  the  list  of  poor  conductors.  Yet  there  is  much  difference  in 
the  ability  of  the  different  fibers  to  conduct  heat.  Wool  is  the 
poorest  conductor,  linen  the  best.  The  "coolest"  clothing  to 
wear  in  summer  is  therefore  made  of  linen,  which  allows  heat 
constantly  to  leave  the  skin. 

The  "  warmth  "  of  fur  and  wool  for  clothing  depends  not  upon 
the  fibers  themselves,  but  upon  the  air  which  is  enclosed  in  all 
the  little  spaces  and  meshes.  Air  is  one  of  the  poorest  con- 
ductors of  heat.  (See  page  278.)  Clothing  containing  air  is 
therefore  the  warmest  to  wear.  An  extra  garment  on  a  cold  day 
adds  not  only  its  thickness,  but  the  layer  of  air  which  is  imprisoned 
beneath  it.  If  the  air  can  be  kept  in  place  by  a  wind-proof  outer 
garment,  it  is  particularly  advantageous.  Have  you  noticed 
how  warm  is  the  combination  of  a  sweater  and  a  raincoat?  A 
light  down  puff  is  a  warmer  bed  covering  than  a  heavier  old- 
fashioned  comforter.  Why? 

Perspiration.  The  human  body  possesses  an  automatic  heat 
regulator  in  the  form  of  the  thousands  of  sweat  glands  which  are 
located  in  the  skin,  especially  abundantly  on  the  palms  of  the 
hands  and  the  soles  of  the  feet.  Each  gland  receives  from  the  cir- 
culating blood  some  of  the  water  and  other  waste  matter  from 
the  body  cells.  (See  page  46.)  The  perspiration,  as  the  liquid 
is  called,  passes  out  upon  the  surface  of  the  skin.  The  tempera- 


CLOTHING  AND  ITS  CARE 


295 


ture  of  the  whole  body  is  thus  kept  constant,  because  when  oxi- 
dation produces  heat  in  each  cell,  some  of  the  heat  as  well  as 
the  waste  matter  is  immediately  dis- 
tributed by  the  circulating  blood.  When 
the  perspiration  reaches  the  skin,  it 
evaporates. 

The  cooling  effect  of  evaporation. 
Why  does  the  wind  chill  us,  while  we 
are  comfortably  warm  on  cooler,  calmer 
days?  It  is  largely  because  the  rate 
of  evaporation  is  increased.  We  are  al- 
ways to  some  extent  perspiring.  The 
sweat  glands  remove  from  the  blood  a 
little  over  a  pint  of  water  and  waste 
matter  every  twenty-four  hours.  We 
are  usually  unconscious  of  the  passage 
of  this  amount,  because  it  is  immedi- 
ately evaporated  into  the  air  or  absorbed 
by  our  clothing. 

After  hard  work  or  exercise,  and  in 
very  hot  weather,  the  amount  of  per- 
spiration is  greatly  increased. 

Air  can  hold  only  a  certain  amount  of  water  vapor,  depending 
upon  its  temperature.  (See  page  108.)  The  warmer  the  air,  the 
greater  amount  of  vapor  it  can  hold.  When  the  air  is  still,  the 
space  just  above  the  surface  of  the  body  becomes  saturated  with 
water  vapor,  so  that  no  more  can  enter,  and  evaporation  is  al- 
most stopped.  When  the  air  is  moving,  the  water  vapor  is 
carried  away  as  fast  as  it  enters  the  air,  and  evaporation  can  go 
on  rapidly. 

Heat  is  taken  from  the  body  when  perspiration  evaporates. 
The  faster  the  evaporation  takes  place,  the  faster  the  body  is 
cooled. 

Clothing  which  is  tightly  woven  keeps  a  layer  of  air  imprisoned 
beneath  it.  This  air  becomes  saturated  with  vapor,  and  prevents 
rapid  evaporation.  In  winter  closely  woven  clothing  is  desirable; 
in  summer  it  is  undesirable.  Loosely  woven  clothing  lets  the  air 


H 


FIG.  148.  A  small  portion  of 
the  skin  (magnified).  £,  sweat 
gland;  H,  hair;  0,  oil  glands; 


296     PROTECTION --HOMES  AND  CLOTHING 

in  and  out,  and  is  therefore  "  cooler  "  to  wear  since  it  allows  rapid 
evaporation. 

The  relation  between  the  color  of  clothes  and  their  warmth. 
Most  of  the  materials  for  our  clothes  absorb  some  colors  in  sun- 
light, and  reflect  others.  (See  page  256.) 

When  all  the  radiant  energy  is  absorbed,  it  is  converted  into 
heat  only.  Black  clothes  therefore  are  warmer  than  colored 
clothes,  especially  in  the  direct  rays  of  the  sun.  White  clothes, 
instead  of  absorbing  the  radiant  energy,  reflect  most  of  it.  You 
can  thus  see  the  scientific  reason  behind  our  choice  of  dark  clothes 
for  winter  and  light  clothes  for  summer. 

Waterproof  clothes.  In  recent  years  a  method  of  making 
goods  waterproof  has  been  perfected.  It  is  called  the  cravenet- 
ting  process.  By  this  means  any  material,  wool,  velvet,  or  silk, 
can  be  so  treated  as  not  to  show  any  spots  of  water.  Although  a 
heavy  rain  will  soak  through  the  goods  treated  in  this  way,  a 
light  shower  will  not  wet  the  goods. 

Makers  of  fibers.  The  fibers  which  come  to  us  from  all  over 
the  world  are  produced  either  by  plants  or  by  animals.  We  may 
classify  them  as  follows: 


Vegetable  fibers 


Animal  fibers 


Cotton 

Flax 

Hemp 

Jute 

Sisal  hemp 

Ramie 

Artificial  silk 


Wool 

Silk 

Fur 


Cotton,  the  leading  plant  fiber.  A  field  of  growing  cotton  is  a 
beautiful  sight,  with  its  tall  plants  covered  with  large  yellow 
flowers,  which  usually  turn  to  red  as  the  seeds  begin  to  ripen. 
The  petals  fall  and  leave  the  seeds  to  ripen  in  a  tightly  closed 
green  pod  or  boll;  finally,  when  the  seeds  are  ripe,  the  boll  opens 
and  reveals  the  snowy  mass  of  cotton. 

The  cotton  fiber  is  nature's  protection  for  the  seed.  Each  fiber 
consists  of  a  single  cell,  fastened  at  one  end  to  the  seed  coat. 


CLOTHING  AND  ITS  CARE 


297 


" 


When  examined  with  a  microscope,  each  cell  is  seen  to  be  a  hol- 
low tube,  flattened  and  twisted,  somewhat  like  a  tiny  fire  hose. 
The  twist  in  the  fiber  makes  it  valuable  for  weaving  into  cloth, 
because  the  hairs  remain  in 
place,  and  help  to  make  the 
cloth  elastic. 

The  advantages  of  cotton 
for  use  as  a  fabric  are  three: 
(i)  it  is  the  cheapest  of  the 
fibers;  (2)  it  can  be  mercerized 
to  resemble  silk  and  finished  to 
resemble  linen  and  even  wool; 
(3)  the  fiber  is  thin  and  fine, 
and  so  can  be  used  for  fine  fab- 
rics suitable  for  hot  climates. 

Flax,  a  plant-stalk  fiber. 
Other  parts  of  plants  besides 
seeds  produce  fibers. 

The  important  plant  fibers, 
aside  from  cotton,  are  pro- 
duced on  the  inside  of  stems. 
The  best-known  is  the  flax, 
which  furnishes  us  our  linen. 


FIG.  149.    Cotton  ready  for  the  picking. 


Flax  belongs  to  the  nettle  family.  It  is  an  annual  plant  which 
grows  from  twenty  to  fifty  inches  high,  and  has  a  lovely  blue 
flower.  Longfellow  has  written  about  a  little  girl,  "  Blue  were 
her  eyes  as  the  fairy  flax."  The  fiber  comes  from  the  inner  bark, 
and  is  composed  of  tiny  cells  in  long  rows  which  help  to  stiffen  the 
bark.  The  fiber  is  nearly  pure  cellulose,  since  it  consists  of  the 
thickened  walls  of  hundreds  of  cells. 

The  advantages  of  linen  as  a  fabric  for  warm  climates  are  two : 
(i)  it  is  the  best  conductor  of  heat  and  therefore  lowers  the  tem- 
perature of  the  body;  (2)  it  does  not  absorb  moisture  or  dirt  as 
readily  as  the  more  spongy  cotton. 

Other  plant  fibers.  The  fiber  which  furnishes  the  cheapest  of 
all  fabrics  is  jute,  which  comes  to  us  from  India  for  the  making 
of  burlap  and  gunny  sacks.  When  jute  is  well  prepared  it  may 


298     PROTECTION  —  HOMES  AND  CLOTHING 

be  mixed  with  silk  to  make  a  cheap  quality  of  silk  fabric.  Some 
is  used,  too,  in  making  carpets  and  rugs. 

The  best  of  all  plant  fibers  is  the  ramie,  or  China  grass.  Per- 
haps you  have  never  heard  of  it.  It  is  twice  as  strong  as  hemp. 
It  is  the  most  rainproof  fiber  known.  It  is  as  beautiful  as  silk. 
It  can  be  raised  in  the  tropical  heat  of  India,  and  the  cool  fields 
of  Normandy.  Yet,  with  all  these  advantages,  ramie  is  used  but 
little,  in  comparison  with  other  fibers.  The  reason  is  the  great 
difficulty  with  which  the  fiber  is  separated  from  the  gummy 
substances  of  the  stalk.  If  some  genius  can  invent  a  machine  to 
perfect  the  separating  process,  he  will  release  to  the  world  a 
fiber  which  will  rival  cotton,  flax,  and  silk  in  popularity  and 
usefulness. 

Wool.  Wool  is  the  under  coat  of  the  sheep.  Originally,  thou- 
sands of  years  ago,  sheep  possessed  an  outer  coat  of  long,  coarse 
hair,  and  an  inner  coat  of  wool.  In  some  hot  countries  sheep 
have  hair  only,  like  deer  or  cows.  The  wool  is  best  developed 
in  cold  countries,  where  it  is  necessary  for  warmth.  By  long 
breeding  and  selection  (see  Project  XVIII)  sheep  have  come  to 
have  a  coat  chiefly  of  wool. 

When  you  look  at  wool  under  a  microscope  you  see  that  it  is 
not  a  one-celled  fiber,  like  cotton,  but  is  composed  of  hundreds  of 
cells  overlapping  like  the  scales  on  a  pine  cone.  The  fact  that 
each  cell  extends  a  little  from  the  fiber  makes  wool  very  valuable 
in  making  cloth,  because  the  fibers  mat  together. 

Woolen  clothing  is  best  for  cold  climates  for  three  reasons;  (i) 
wool  is  a  poorer  conductor  of  heat  than  the  other  fibers;  (2)  it 
absorbs  the  moisture  from  the  skin  by  capillary  action  in  its  tiny 
tube-like  fibers  and  in  the  spaces  between  the  woven  threads; 
(3)  it  does  not  become  wet  from  rain  so  easily  as  do  other  fabrics. 

Silk.  The  story  of  a  Chinese  empress  who  lived  before  2500  B.C.  is  the 
story  of  the  beginning  of  our  knowledge  of  silk.  One  day  when  she  was 
walking  in  the  palace  garden  she  discovered  a  strange  and  ugly  "worm." 
It  was  small,  pale  green  in  color,  and  was  feeding  greedily  on  a  mulberry 
leaf.  Instead  of  screaming  and  running  away  from  the  ugly  creature,  she 
called  the  Emperor,  and  together  they  watched  the  insect  until  finally  it 
spun  a  fine  silken  web.  The  story  goes  that  it  was  the  Empress  who  took 
the  web  and  succeeded  in  reeling  the  filament  from  it  and  weaving  it  into 


CLOTHING  AND  ITS  CARE 


299 


silk.  To  this  day  she  is  called  the  "  Goddess  of  the  Silkworm,"  and  a  feast 
in  her  honor  is  celebrated  every  year  at  the  season  when  the  silkworm  eggs 
are  hatched. 

The  silkworm  is  really  not  a  worm  at  all,  but  one  of  the  stages 
in  the  life  of  a  moth.  Like  all  moths  and  butterflies,  the  insect 
passes  through  four  stages  before  its  life  is  complete,  the  egg, 
the  caterpillar,  the  pupa, 
and  the  adult  moth.  It  is 
in  its  preparation  for  the 
pupa  stage  that  the  silk- 
worm makes  the  wonder- 
ful silk  filament.  First  the 
worm  loses  its  appetite, 
shrinks  nearly  an  inch, 
and  restlessly  hunts  for  a 
place  to  attach  the  first 
threads  of  the  cocoon 
which  is  to  cover  it  while 
it  passes  through  its  trans- 
formation. 

The  silk  is  made  in  the 
body  of  the  caterpillar, 
from  the  pulpy  mass  of 
mulberry  leaves.  Special 
glands  in  the  head  contain  the  jelly-like  mass  which  is  drawn 
from  a  tiny  double  opening  below  the  mouth.  As  soon  as  it 
reaches  the  air  it  hardens  into  a  yellowish  thread.  You  would 
be  particularly  interested  in  watching  the  caterpillar  spin,  for 
it  moves  its  head  incessantly,  sixty-five  times  in  a  minute,  and 
keeps  up  its  work  for  about  three  days.  When  the  worm  has 
finished  spinning,  it  is  only  a  little  over  an  inch  long.  It  is  en- 
tirely protected  in  a  silken  case  which  is  tough  and  waterproof. 

It  takes  nearly  three  thousand  cocoons  to  make  a  pound  of 
reeled  silk.  Laborers  must  watch  every  stage  and  must  reel  the 
silk  from  the  cocoon  largely  by  hand.  Only  in  countries  like 
China,  Japan,  and  India,  where  labor  is  plentiful  and  cheap,  can 
silkworms  be  profitably  raised. 


FIG.  150.  A  scene  in  China  centuries  ago.    Feeding 
the  young  silkworms. 

(Courtesy,  Cheney  Brothers.) 


300    PROTECTION  —  HOMES  AND  CLOTHING 


The  advantages  of  silk  for  clothing  are  three:  (i)  it  is  the  most 
beautiful  of  all  the  fibers ;  (2)  it  is  a  better  conductor  of  heat  than 

cotton  or  wool,  thus  mak- 
ing a  good  fabric  for  hot 
climates;  (3)  the  fiber  is 
so  smooth  that  it  keeps 
clean  better  than  the 
rougher  wool,  cotton,  and 
linen. 

Artificial  silk.  An  interest- 
ing fabric  has  been  recently 
invented  to  compete  with  silk. 
Silkworms  transform  the  cells 
of  the  mulberry  leaves  into 
the  beautiful  silk  fiber  by 
means  of  chemical  processes 
which  take  place  within  their 
bodies.  Chemists  have  learned 
to  imitate  this  process.  They 
use  other  vegetable  cells,  saw- 
dust or  cotton  waste,  trans- 
form them  by  chemical  proc- 
esses into  a  jelly-like  mass, 
and  convert  it  into  delicate 
fibers  by  driving  it  through 
very  small  holes  in  a  glass 
screen.  The  filaments  can  be 
reeled  and  woven  like  real 
silk.  Perhaps  you  are  wear- 
ing clothes  made  of  artificial 
silk,  for  already  this  new  fabric  is  used  one  fourth  as  much  as  silk. 


FIG.  151.  Boiling  cocoons  and  reeling  silk  in  a 
great  modern  silk  factory  in  Japan.  These  girls 
work  long  hours  every  day  for  a  few  cents.  Much 
of  the  labor  must  be  done  by  hand. 

(Copyright,  Keystone  View  Co.) 


Other  animal  resources  for  clothing.  The  earliest  clothing 
worn  by  man  was  probably  the  skin  of  some  animal.  Through 
all  the  ages  we  have  valued  skins.  The  thick  hides,  windproof, 
largely  waterproof,  and  durable,  furnish  us  our  shoes,  our  gloves, 
and  in  many  cases  coats,  vests,  and  caps  of  leather.  The  fur, 
warm  because  of  the  air  held  between  the  hairs,  is  the  best  winter 
clothing  we  have. 

The  care  of  our  clothing.    When  you  have  a  new  suit,  you  are 


CLOTHING  AND  ITS  CARE 


301 


very  careful  at  first  to  keep  it  fresh,  clean,  and  free  from  spots. 
The  attractiveness  of  your  appearance  depends  largely  upon  the 
condition  of  your  clothes.  Equally  important  is  the  fact  that 
your  comfort  and  health  often  depend  upon  the  condition  of  your 
clothing.  Soiled  garments  which  are  filled  with  perspiration, 
containing  the  waste  matter  of  the  body, 
become  stiff  and  rough  and  thus  may 
irritate  the  skin.  Soiled  garments  are  es- 
pecially dangerous  if  there  is  the  slight- 
est cut  or  eruption  on  the  skin.  It  is 
well  worth  while,  therefore,  for  every  one 
to  know  how  to  keep  his  clothing  clean 
and  free  from  spots. 

Water  as  a  cleanser.  The  great  cleanser 
is  water.  Washing  is  never  satisfactory  un- 
less water  is  used  in  abundance.  It  should 
be  clean  and  soft.  Rain  water  is  always 
soft,  because  it  contains  no  salts  in  solution. 

If  the  water  is  hard  (see  page  93),  it 
can  be  softened  by  boiling,  or,  in  the  case 
of  permanent  hardness,  by  the  addition 
of  borax,  ammonia,  washing  soda,  or  a 
large  amount  of  soap. 

The  action  of  soap.  The  secret  of  soap-making  has  been  known 
to  the  human  race  since  very  early  times.  Indeed,  the  process  is 
no  secret ;  it  may  be  briefly  expressed  thus : 

Fat  +  lye  =  soap  +  glycerine. 

Fats  are  obtained  from  animals  and  from  certain  vegetables, 
as  the  olive  oil,  palm  oil,  and  cotton-seed  oil.  Lye  is  a  product 
made  by  treating  wood  ashes  with  lime.  When  combined  in  just 
the  right  proportion,  the  fat  and  the  lye  act  on  each  other  chem- 
ically and  produce  the  new  products,  soap  and  glycerine. 

When  soap  is  used  for  cleansing  purposes,  its  value  is  chiefly 
in  removing  grease.  If  you  cover  your  hands  with  grease,  and 
try  to  clean  them  by  holding  them  under  running  water,  you  will 
find  that  they  are  still  greasy.  If  you  rub  them  with  soap,  how- 


FIG.  152.  A  little  Eskimo 
girl  clad  in  furs  and  bird- 
skins. 

(Courtesy,  American  Museum 
of  Natural  History,  N.  Y.) 


302     PROTECTION  —  HOMES  AND  CLOTHING 

ever,  and  rinse  them  with  running  water,  you  can  cleanse  them 
quickly  and  easily.  The  soap  breaks  up  the  oil  or  grease  into 
small  drops,  coats  each  with  a  fine  soap  film,  and  so  enables  the 
water  to  wash  them  easily  off  the  hands.  With  the  droplets  of 
oil  goes  any  dirt  which  has  become  attached  to  the  skin.  Oil  or 
grease  which  is  broken  up  into  small  droplets  is  called  an  emulsion. 
The  value  of  soap  is  that  it  forms  an  emulsion  with  oils. 


FIG.  153.  A  kettle  of  soap  in  the  making.  This  kettle  holds  350,000  pounds 
of  soap,  enough  to  fill  ten  freight  cars.  During  the  two  weeks  that  the  soap  re- 
mains in  the  kettle,  it  is  boiled  several  times,  and  a  chemical  change  takes  place 
which  transforms  the  fat  and  alkali  into  soap  and  glycerine.  The  glycerine  is 
drawn  off  from  the  bottom  of  the  kettle  and  the  soap  is  drawn  off  from  the  top. 

(Courtesy,  Scientific  American.) 

How  to  remove  stains.  Four  general  methods  of  removing 
stains  are  in  use :  solution,  absorption,  bleaching,  and  neutralization. 

i.  By  solution.  The  commonest  way  of  removing  stains  is  by 
dissolving  the  stain  in  some  solvent.  Remember  that  to  remove 
a  stain  takes  time.  Do  not  expect  any  solvent  to  remove  a  stain 
in  an  instant.  You  must  use  plenty  of  the  liquid,  and  you  must 
be  sure  to  remove  all  the  solution  from  the  fabric;  otherwise  you 
will  not  remove  the  stain,  but  spread  it.  The  best  way  is  to  start 
at  the  edge  of  the  spot,  and  work  towards  the  center. 


CLOTHING  AND  ITS  CARE 


303 


The  following  table  shows  the  proper  solvent  to  use  in  certain 
cases : 


STAINS  REMOVED  BY  SOLUTION 


Stain 


Blood. 


Solvent 
Water,  cold. 


Directions 


Coffee  and  tea.      Water. 


Color  from  other 
articles. 
Fly  paper. 
Fruit  stains. 

Water. 

Benzine. 
Water. 

Grass  stains. 

Grease. 
Machine  oil. 
Ink. 

Water. 
Alcohol. 
Water. 
Water. 
Milk  and  benzine. 

Turpentine. 


Soak  in  salt  water;  wash  with  warm 

water  and  soap;  boil. 
Hold  over  bowl  and  pour  boiling  water 
through.     If  stain  is  set,  put  salts  of 
lemon  on  stain,  and  pour  boiling 
water  through. 
Soak  in  cold  water  twelve  hours;  dry 

in  sun. 

Sponge  with  plenty  of  benzine. 
Use  boiling  water  over  bowl.     If  set, 

use  Javelle  water. 
Use   cold    water   without    soap.       If 

stains  are  set,  dissolve  in  alcohol. 
Wash  in  warm  water  and  soap. 
Use  cold  water,  ammonia,  and  soap. 
Sponge  with  milk  until  ink  is  removed, 
then  use  benzine  to  remove  grease 
of  milk.   . 
Soak  spots  several  hours,  then  rub 

with  hands. 

(Note  —  Inks  differ  in  composition.     One  treatment  may  remove  one  kind 
of  spot  and  fail  to  touch  another  ink  spot.) 
Iodine.  Alcohol.  Wash  with  alcohol,  and  rinse  in  soapy 

water,  then  clear  water. 

Paint.  Turpentine.  Sponge  with  plenty  of  turpentine. 

Perspiration.          Water.  Soak  stain  in  cold  water,  wash  with 

borax  and  expose  to  sunshine. 

Rust.  Benzine.  Use  mixture  of  benzine  and  borax. 

Tar.  Turpentine.  Rub  turpentine  in;  wash  in  water  or 

benzine. 

2.  By  absorption.  The  secret  of  removing  stains  by  absorption 
is  capillary  action,  which  draws  the  stain  up  into  the  absorbent. 
(See  page  134.)  Grease  spots  are  most  commonly  removed  in 
this  way.  The  absorbents  used  are  blotting-paper ;  a  paste  made 
of  starch  and  gasoline,  or  water;  French  chalk;  lard.  Heat  from 
a  flat  iron  is  often  used  to  melt  the  grease  to  a  liquid. 


STAINS  REMOVED  BY  ABSORPTION 

Stain  Absorbent  Directions 

Blood.  Starch  paste.  For  blood  stains  on  heavy  materials, 

apply  a  paste  of  starch  and  warm 
water,  let  dry,  and  brush  off. 


304    PROTECTION  —  HOMES  AND  CLOTHING 


Stain 
Grease. 

Machine  oil. 

Ink. 

Mildew. 

Scorch. 
Tar. 


A bsorbent 
French  chalk. 

Lard. 

Tallow  or  paraffin. 

Paste  of  soap  and 
chalk. 


Starch  paste. 
Lard. 


Directions 
Put  chalk  over  spot,  and  hold  hot  iron 

over  chalk. 
Cover  spots  with  lard;  let  stand;  wash 

in  cold  water  and  soap. 
Dip   fabric    in    melted    tallow;    then 

wash  with  soap  and  warm  water. 
Make  paste  of  2  parts  soft  soap,  2 

parts  of  water,  and  I  of  chalk.  Rub 

into  goods.     Keep  damp  until  stain 

disappears. 
Make  paste  of  boiled  starch,  let  dry 

on,  and  wash. 
Cover  stain  with  lard;  after  several 

hours,  wash. 


j.  By  bleaching.  Stains  which  cannot  be  dissolved  or  absorbed 
may  sometimes  be  bleached.  Housewives  have  long  known  the 
bleaching  action  of  the  air,  sun,  and  dew.  Sulphur  burned  to  form 
sulphur  dioxide  fumes  may  be  used  to  bleach  straw  hats  and  silk 
or  wool  cloth.  A  common  household  bleaching  agent  is  Javelle 
water,  which  sets  free  some  of  the  gas  chlorine,  which  has  strong 
bleaching  powers.  For  directions  for  making  Javelle  water,  see 
problem  13  on  page  292.  It  may  be  used  only  on  white  goods. 


STAINS  REMOVED  BY  BLEACHING 


Stain 


Fruit. 

Fruit. 
Peach. 


Grass. 


Bleaching  agent 
Javelle  water. 

Sulphur  dioxide. 
Salts  of  lemon  and 
sun. 

Javelle  water. 


Ink  or  rust  on    Lemon    juice    and 
white  goods.  sun. 

Hectograph  ink.     Cream  of  tartar  and 
sun. 


Indelible  ink.         Javelle  water. 
Mildew.  Javelle  water. 

Perspiration.          Javelle  water. 


Directions 
Use   equal   quantities  Javelle   water 

and  water  with  little  vinegar. 
Hold  stain  over  fumes  of  sulphur. 
Moisten  spot,  rub  in  salts  of  lemon, 

leave  in  sun.     Wash  with  salt  and 

warm  water. 
Use  equal   parts   water  and   Javelle 

water. 
Cover    spot    with    salt.       Rub    with 

lemon   juice;   lay   in   sun.      Rinse 

with  cold  water. 
Boil  in  strong  cream  of  tartar  water. 

Rinse,  lay  in  sun,  keeping  it  wet 

with  cream  of  tartar  water.     Soak 

over   night   in   sour   milk.      Rinse 

next    morning    and    sun    all    day. 

Wash. 
Use  equal   parts  water  and  Javelle 

water.     Rinse  well. 
Wet  the  stain  with  Javelle  water,  lay 

in  sun.     Keep  moist.     Rinse. 
Use  one  part  Javelle  water  to  four 

parts  hot  water. 


CLOTHING  AND  ITS  CARE  305 

Stain  Bleaching  agent  Directions 

Rust.  Javelle  water.  Use  equal   parts  water  and  Javelle 

water. 

"Yellowed"  Kerosene.  Mix  equal   parts  of  kerosene,   clear 

white  clothes.  lime  water,  and  turpentine,  shaken 

until   creamy.      Add    I    cupful   to 
boilerful  of  clothes. 

4.  By  neutralization.  A  fourth  method  of  removing  spots  is  by 
neutralization.  If  you  apply  the  simple  litmus  paper  test,  you 
find  that  all  the  substances  which  you  test  are  either  acid,  alka- 
line, or  neutral.  Acids  and  alkalies  are  exactly  opposite  in  char- 
acter and  when  put  together  in  the  right  proportion  they  produce 
a  neutral  substance.  Spots  are  often  caused  by  acids  and  alka- 
lies. The  treatment  is  to  apply  the  opposite  kind  of  a  substance. 

STAINS  REMOVED  BY  NEUTRALIZATION 

Stain  Directions 

Acid.  The  stain  usually  turns  red.      Rub 

gently  with  dilute  ammonia. 

Vinegar.  Wash  in  ammonia  water. 

Lime,  lye,  or  washing  soda.  Drop  vinegar,  lemon  juice  or  oxalic 

acid  on  spot,  and  wash  with  water. 

Clothes  moths.  One  of  the  housewife's  greatest  enemies  is  the 
clothes  moth.  Like  all  moths,  this  pest  passes  through  four 
stages  in  its  life  history.  The  eggs  are  laid  by  the  adult  female 
moths  on  clothing,  especially  wool  and  fur.  When  the  eggs 
hatch,  the  larvce,  or  tiny  caterpillars,  proceed  to  eat  the  fibers  of 
wool  or  fur.  We  are  all  familiar  with  the  "moth  hole"  which 
results.  After  the  larva  is  full  grown,  it  changes  to  a  pupa  and 
finally  to  the  adult. 

By  the  use  of  camphor  balls  and  cedar  bags  moths  may  be  kept 
from  attacking  clothing.  Be  sure  to  hang  all  winter  clothing  in 
the  sun  for  several  hours  and  brush  carefully  before  putting  away 
for  the  summer.  If  there  are  no  moth  eggs  upon  them,  garments 
may  be  kept  safely  in  newspaper,  sealed  air-tight  by  paste  or  glue, 
or  in  unbleached  muslin. 

INDIVIDUAL  PROJECTS 

Working  projects: 

i.  Make  a  collection  of  cotton  materials  used  for  clothing.  Cut  the  samples 
to  the  same  size,  and  mount  them  on  cards.  Under  each  sample  print  the 
name,  the  width,  and  the  price. 


306    PROTECTION  —  HOMES  AND  CLOTHING 

2.  Make  a  similar  collection  of  woolen  materials. 

3.  Make  a  collection  of  linen  materials. 

4.  Make  a  collection  of  silk  materials. 

5.  Make  a  collection  of  materials  containing  two  kinds  of  fibers. 

6.  Dye  a  garment,  following  directions  which  accompany  the  dye. 

Reports: 

1.  Uses  of  the  cotton  plant. 

2.  The  great  cotton-producing  regions  of  the  world. 

3.  How  flax  fibers  are  prepared. 

4.  The  history  of  the  use  of  wool  for  clothing. 

5.  How  better  wool  is  obtained  by  breeding  and  selection. 

6.  The  silk  industry  in  Japan. 

7.  The  life  history  of  a  silkworm. 

8.  Eli  Whitney  and  the  cotton  gin. 

BOOKS  THAT  WILL  HELP  YOU 

Asia.     N.  B.  Allen.     Ginn  &  Co. 

Silkworms  and  silk  manufacturing. 
The  Book  of  Wonders.     Presbrey  Syndicate,  New  York. 

Includes  accounts  of  wool,  silk,  and  cotton. 

Dyestuffs.    February,  1918.     National  Anilene  and  Chemical  Co.,  244  Madi- 
son Ave.,  New  York. 

This  number  of  the  magazine  contains  an  account  of  waterproofing  proc- 


Europe.     N.  B.  Allen.    Ginn  &  Co. 

Chapters  on   "The  Queen  of  Fibers  (Silk)";    "Flax  and  other  Fibers, 
and  the  Countries  which  Produce  Them." 
From  Wool  to  Cloth.    American  Woolen  Co.,  Boston. 

A  well-illustrated  booklet  to  be  obtained  free  on  application. 
Great  Inventors  and  their  Inventions.     F.  P.  Bachman.     American  Book  Co. 

Eli  Whitney,  inventor  of  the  cotton  gin. 
How  the  World  is  Clothed.     F.  G.  Carpenter.     American  Book  Co. 

Journeys  to  lands  where  clothing  materials  are  grown  and  manufactured. 
Shelter  and  Clothing.     Kinne  and  Cooley.     The  Macmillan  Co. 
The  Story  of  Silk.     H.  H.  Manchester.     Cheney  Brothers,  Fourth  Ave.  and 
i8th  St.,  New  York. 

An  illustrated  booklet,  free  on  request. 
The  Story  of  Wool.     Bassett.     Pennsylvania  Publishing  Co. 
The  United  States.    I.  O.  Winslow.    D.  C.  Heath  &  Co. 

Includes  a  description  of  the  cotton  industry. 
The  World's  Commercial  Products.     Freeman  and  Chandler.    Ginn  &  Co. 

Foods,  fibers,  dyes,  etc. 


UNIT  V 
THE  WORK  OF  THE  WORLD 


PROJECT  XV 
WORK  WITH  EVERYDAY  MACHINES 

Machines  in  our  homes.  If  you  were  obliged  to  do  all  the  work 
of  your  home  without  a  machine  to  help  you,  you  would  find  that 
you  could  accomplish  very  little.  In  the  first  place,  your  home 
in  a  machineless  world  would  be  very  different  from  what  it  now 
is.  It  could  not  be  built  of  wood,  for  there  would  be  no  saws  nor 
axes  to  cut  the  wood;  it  might  be  a  cave,  or  a  hut  constructed  of 
natural  field  stone  plastered  together  with  mud.  Your  table 
manners  would  be  very  poor;  you  would  be  obliged  to  use  your 
fingers  entirely,  since  knives,  forks,  and  spoons  are  machines. 
Even  the  crude  flint  knife  of  the  Indian  is  a  machine.  Your  food 
could  consist  only  of  berries,  and  roots  pulled  from  the  ground, 
with  what  birds,  fish,  and  small  animals  you  could  catch  with 
your  hands.  For  clothing  you  would  be  obliged  to  depend  on 
leaves  or  bark  from  trees.  You  would  in  fact  be  a  savage  of  a 
very  low  order. 

Contrast  with  that  picture  the  homes  in  a  modern  city.  Built 
of  brick,  cement,  and  steel  which  themselves  require  complicated 
machinery  for  their  making,  they  tower  high  above  the  streets 
where  electric  cars,  great  motor  trucks,  and  pleasure  cars  swiftly 
pass.  Over  the  heads  of  pedestrians  or  in  underground  conduits 
are  wires  transporting  power  from  distant  stations  to  run  the 
vast  machinery  of  the  city.  Pianos,  elevators,  telephones,  light- 
ing systems,  and  countless  other  devices  of  our  modern  homes  are 
themselves  machines  and  depend  upon  machinery  for  their  opera- 
tion. 

Even  the  humblest  cottage  in  the  country  contains  many 
machines.  The  nails  and  screws  which  fasten  the  house  together, 


308  THE  WORK  OF  THE  WORLD 

the  doorknob  or  latch,  the  axe,  the  grindstone,  the  wheelbarrow, 
the  plough,  the  hoe,  the  spade,  the  shears,  all  are  machines.  We 
live,  as  has  been  said,  in  an  Age  of  Machinery. 

Most  boys  are  interested  in  machines.  To  some  girls,  however, 
a  machine  seems  a  remote,  puzzling  thing,  an  understanding  of 
which  is  not  needed  in  their  daily  life.  Yet  such  is  not  the  fact. 
Many  of  the  machines  used  in  the  problems  which  follow  are 
household  machines,  which  they  must  understand  to  use  intelli- 
gently. 

PROBLEM  i :  WHAT  ARE  THE  CAUSES  OF  RESISTANCE  TO  WORK? 

Directions : 

1.  Try  to  lift  various  articles  in  the  room.    Are  you  able  to  lift  them  all? 
Give  reasons. 

2.  Set  various  articles,  such  as  an  eraser,  a  ball,  a  stone,  a  ruler,  etc.,  in  a 
row  on  the  floor  or  on  a  large  table.     By  means  of  a  yard-stick  or  meter- 
stick  push  them  all  with  equal  force.     Do  they  all  move  the  same  distance? 
Give  reasons. 

3.  Place  a  card  over  an  upturned  glass  with  a  coin  in  the  center  of  the 
card.    Snap  the  card  aside.    What  is  the  result?   Which  was  stronger,  the 
force  applied  to  the  card,  or  the  inertia  of  the  coin?     (See  page  321.) 

Roll  a  heavy  ball  along  the  floor.  With  a  ruler  strike  it  sharply  at  right 
angles  to  its  direction  of  motion.  What  is  the  result?  Which  is  stronger, 
the  force  applied  at  right  angles  or  the  inertia  of  the  moving  ball? 

Conclusion : 
Name  three  causes  of  resistance. 

Questions  : 

1.  Why  is  sand  put  on  icy  sidewalks? 

2.  Why  do  cars  slip  on  rails  which  are  covered  with  leaves? 

3.  Why  do  chains  on  automobile  tires  prevent  skidding? 

4.  Why  do  automobiles  skid  more  in  turning  corners  than  when  going 
ahead? 

5.  Why  should  the  working  parts  of  an  automobile  motor  be  kept  im- 
mersed in  oil? 

PROBLEM  2:  To  FIND  MACHINES  IN  THE  SCHOOLROOM. 
Directions: 

Do  you  see  any  machines  in  the  schoolroom?    Name  them. 

(Note  —  A  machine,  as  scientists  understand  the  term,  is  any  device 

which  lightens  the  labor  of  man,  or  gives  him  more  efficiency  to  do  his 

work.) 

What  devices  can  you  now  find  in  the  schoolroom  which  are  machines, 
according  to  this  definition? 


WORK  WITH  EVERYDAY  MACHINES      309 

PROBLEM  3:  WHAT  MACHINES  ARE  USED  IN  MY  HOME? 

Directions  : 

Examine  the  different  rooms  in  your  house,  and  their  furnishings,  to  dis- 
cover the  machines  which  are  used  to  help  do  the  work  of  the  house.  Clas- 
sify in  the  following  way  the  machines  found : 

1.  Machines  in  the  kitchen  and  pantry. 

2.  Machines  in  the  dining-room. 

3.  Machines  in  the  living-rooms. 

4.  Machines  in  the  bedrooms. 

5.  Machines  in  other  parts  of  the  house. 

6.  Machines  used  out-of-doors. 

7.  Machines  used  in  barn  or  garage. 

Summary: 

1.  How  many  different  kinds  of  machines  did  you  find  in  your  house? 

2.  How  many  were  found  by  the  class  as  a  whole? 

3.  In  what  kinds  of  work  do  machines  help? 

(Note  to  the  teacher  —  This  problem  may  be  made  a  game  by  counting 
on  the  score  of  each  pupil  who  found  a  machine  one  point  for  each  mem- 
ber of  the  class  who  did  not  find  the  machine  named.) 

PROBLEM  4:  To  STUDY  A  SIMPLE  MACHINE,  THE  LEVER. 

Directions : 

Hang  from  a  support  a  meter-stick  or  yard-stick  which  is  painted  with 
alternate  units  black. 

Let  one  pupil  hang  two  weights  from  the  stick  in  such  a  way  that  the 
stick  balances. 

Make  a  record  of  what  the  weights  are,  and  how  far  away  from  the 
balancing  point  they  are  hung. 

Let  another  pupil  arrange  the  apparatus  to  balance  in  another  way. 
Try  as  many  arrangements  and  combinations  of  weights  as  possible.  • 

The  meter-stick  may  be  considered  a  lever,  which  is  defined  as  "  a  rod  free 
to  turn  about  a  point."  Call  the  point  about  which  it  turns  the  fulcrum; 
call  one  weight  the  acting  force,  the  other  weight  the  resisting  force.  Call 
the  distance  from  the  fulcrum  to  the  acting  force  the  force  arm,  and  the 
distance  from  the  fulcrum  to  the  resisting  force  the  resistance  arm. 

Record  the  results  in  a  table,  as  follows: 


Acting  force 

Force  arm 
Fa, 

Resisting  force 
R. 

Resistance  arm 
Ra. 

F.XFa. 

R.  X  Ra. 

3io  THE  WORK  OF  THE  WORLD 

Conclusion: 
What  is  the  law  of  the  lever? 

Question : 

Why  will  a  seesaw  not  work  well  if  a  child  and  a  grown  person  sit  equally 
distant  from  the  support?  Where  should  they  sit? 

PROBLEM  5:  WHAT  ARE  THE  ADVANTAGES  OF  USING  A  LEVER? 

Directions: 

Make  a  lever  with  a  meter-stick  or  a  ruler.  Use  a  heavy  weight  for  the 
resistance  and  your  hand  to  apply  the  acting  force. 

Place  the  weight  at  one  end  of  the  lever,  the  fulcrum  near  it,  and  bal- 
ance it  with  your  hand  at  the  other  end.  Can  you  lift  the  weight  easily? 
Does  the  weight  or  your  hand  move  faster?  Which  moves  farther? 

What  is  gained  by  using  a  lever  of  this  kind? 

Now  place  the  fulcrum  near  your  hand,  so  that  the  force  arm  is  short  and 
resistance  arm  long.  Can  you  support  the  weight  as  easily  as  before?  Is 
the  weight  easy  to  lift?  Which  moves  faster,  your  hand  or  the  weight? 
Which  moves  farther? 

What  is  gained  by  using  a  lever  of  this  kind? 

Conclusion: 
What  are  two  advantages  of  a  lever? 

PROBLEM  6:  To  WEIGH  AN  ARTICLE. 

Directions: 

Use  either  a  platform  balance  or  a  horn  balance. 

Explain  how  this  machine  is  a  lever.  Where  are  the  fulcrum,  the  arms, 
the  acting  force,  and  the  resisting  force? 

Place  some  object  such  as  a  heavy  stone  in  one  scale  pan.  Balance  it 
with  weights  in  the  other  pan.  Explain  how  you  can  find  in  this  way  the 
weight  of  any  object. 

Let  different  pupils  weigh  articles  and  write  the  weights  on  the  board. 

PROBLEM  7 :  To  STUDY  THREE  TYPES  OF  LEVERS. 

(Note  —  Any  of  the  three  forces  acting  on  a  lever  may  be  made  its 

fulcrum.) 

A  lever  of  the  first  type  has  the  fulcrum  between  the  acting  force  and 
the  resistance.  (See  figure  164.) 

A  lever  of  the  second  type  has  the  resistance  between  the  fulcrum  and 
the  acting  force.  (See  figure  165.) 

A  lever  of  the  third  type  has  the  acting  force  between  the  fulcrum  and 
the  resistance.  (See  figure  166.) 


WORK  WITH  EVERYDAY  MACHINES      311 

Directions: 

Part  i.  Examine  a  pair  of  scissors.  Cut  something.  Where  is  the  ful- 
crum? Where  is  the  resistance?  Where  is  the  acting  force  applied? 

Sketch  the  scissors,  labeling  fulcrum,  resistance,  resistance  arm,  acting 
force,  force  arm. 

Why  are  the  blades  of  paper  cutting  scissors  so  much  longer  than  blades 
of  wire  cutting  shears? 

Use  a  ruler  as  a  first  type  lever  to  lift  a  book. 

Part  2.    Examine  a  nut-cracker  or  potato  masher.    Where  is  the  fulcrum, 
the  acting  force,  the  resistance?     Sketch,  labeling  the  parts  of  the  lever. 
Lift  a  book  with  a  ruler  used  as  a  second  type  lever. 

Part  3.  Examine  a  sugar  tongs  or  fire  tongs.  Where  is  the  fulcrum, 
the  resistance,  the  acting  force?  Sketch,  labeling  the  parts  of  the  lever. 

Summary: 

1.  What  are  the  parts  of  every  lever? 

2.  Which  type  of  lever  always  needs  an  acting  force  greater  than  the 
resistance? 

3.  Which  type  uses  an  acting  force  smaller  than  the  resistance? 

Home  Work: 

What  levers  are  used  in  my  home? 

Directions: 

Classify  the  levers  of  the  first,  second,  and  third  types  which"  you  find 
in  use  in  your  home. 

(This  problem  may  be  considered  a  game  by  counting  as  suggested  in 

the  introductory  problem.) 

PROBLEM  8:  To  STUDY  A  CRANK  AND  AXLE  MACHINE,  THE  EGG-BEATER. 

Directions: 

Part  i.     Examine  the  way  that  a  Dover  egg-beater  works. 

Show  how  the  wheel  of  the  egg-beater  is  a  modified  lever.  Where  is  the 
fulcrum,  the  acting  force,  the  resistance?  What  type  of  lever  does  the 
wheel  of  the  egg-beater  represent? 

Part  2.  The  advantage  of  the  egg-beater  is  increased  by  means  of  an- 
other modification  of  the  lever,  the  cogwheels  or  gears. 

Examine  the  small  cogwheel.  Where  is  the  resistance?  What  is  the 
cause  of  the  resistance  in  this  case?  What  type  of  lever  does  the  cogwheel 
represent? 

How  many  revolutions  does  the  blade  of  the  egg-beater  make  while  the 
wheel  is  making  one  revolution? 

Count  the  cogs  in  the  large  wheel ;  in  the  small  wheel.  What  is  the  rela- 
tion between  them? 


312 


THE  WORK  OF  THE  WORLD 


Summary: 

1.  Explain  the  resemblance  of  a  crank  and  axle  to  a  lever. 

2.  Show  how  a  cogwheel  is  a  modified  crank  and  axle,  and  therefore  a 
modified  lever. 

3.  How  may  the  mechanical  advantage  of  a  system  of  cogwheels  be 
found? 

Question: 
Why  does  rapidly  turning  an  egg-beater  clean  it? 

Home  Work: 

What  crank  and  axle  machines  are  used  at  home? 

Make  a  list  of  all  the  machines  found  in  the  house, 
barn,  or  garage,  which  depend  on  the  principle  of 
the  crank  and  axle. 

PROBLEM  9:  How  DO  PULLEYS  WORK? 

Directions: 

Part  i.  The  fixed  pulley. 

Attach  a  single  pulley  to  some  support.  Weigh 
a  heavy  stone.  Fasten  a  cord  to  the  stone,  and  pass 
the  free  cord  over  the  pul- 
ley. Attach  this  end  to  a 
spring  balance. 

Pull  down  on  the  bal- 
ance. What  is  the  effect 
on  the  stone?  What  is 
the  reading  of  the  balance? 

How  may  the  pulley  be 
considered  a  modified  lev- 
er? Sketch,  labeling  the 
parts  of  the  lever.  What 
type  of  lever  is  the  fixed 
pulley? 

How    does    the    acting 
force    compare  with    the 
resistance? 
What  is  the  advantage  of  a  fixed  pulley? 

Part  2.    The  movable  pulley. 

Detach  the  pulley  and  fasten  the  stone  to  it.   FIG.  155.  A  movable  pulley 
Fasten  one  end  of  the  cord  to  the  support  and 

pass  the  other  end  through  the  pulley  to  the  hook  of  the  spring  balance. 
Raise  the  stone  by  pulling  up  with  the  spring  balance. 

What  is  the  weight  of  the  stone? 

What  is  the  reading  of  the  spring  balance? 


FIG.  154.  A  fixed  pulley. 


WORK  WITH  EVERYDAY  MACHINES      313 

Where  is  the  fulcrum  of  the  lever? 
Where  is  the  acting  force  applied? 
Where  is  the  resistance? 

How  does  the  force  arm  compare  with  the  resistance  arm? 
How  does  the  distance  that  the  stone  is  raised  compare  with  the  dis- 
tance that  the  acting  force  moves? 
Sketch,  labeling  all  parts  of  the  lever. 

Part  3.     Combinations  of  pulleys. 

Arrange  a  combination  of  fixed  and  movable  pulleys,  as  follows:  Attach 
the  fixed  block  of  pulleys  to  a  support.  Fasten  the  cord  to  the  fixed  block, 
then  pass  it  over  one  pulley  in  the  movable 
block,  one  in  the  fixed  block,  etc.  To  the  end  of 
the  cord  attach  a  spring  balance.  Attach  the 
weight  to  the  hook  on  the  movable  block. 

Now  pull  with  the  spring  balance.  What  is 
the  weight?  What  is  the  acting  force  that  must 
be  applied  to  lift  the  weight? 

How  many  strands  of  cord  support  the 
weight? 

How  does  the  distance  which  the  weight  moves 
compare  with  the  distance  which  the  acting  force 
moves? 

Can  you  arrange  a  system  of  pulleys  so  that  a 
girl  in  the  class  can  lift  a  boy? 

Summary: 

1.  How  may  a  pulley  be  considered  a  lever? 

2.  Has  a  fixed  or  a  movable  pulley  a  greater 
mechanical  advantage? 

3.  How  may  the  mechanical  advantage  of  a 
combination  of  pulleys  be  determined? 

Questions: 

1.  Where  are  pulleys  used  in  your  home? 

2.  How  are   pulleys  used  when  furniture  is     FlG- 15&  A  combination  of 
moved?  pulleys. 

3.  Where  else  have  you  seen  pulleys  in  use? 

4.  How  heavy  must  each  window  weight  be  in  order  to  hold  up  a  win- 
dow which  weighs  20  pounds? 

PROBLEM  10:  To  USE  AN  INCLINED  PLANE  AND  FIND  ITS  ADVANTAGE. 

Directions: 

Rest  one  end  of  a  smooth  long  board  on  the  table.     Support  the  other 
end  above  the  table,  so  that  the  height  of  the  upper  end  of  the  inclined 


314 


THE  WORK  OF  THE  WORLD 


plane  is  one  half  the  length  of  the  inclined  plane.  In  a  toy  car  which 
runs  easily  place  weights  or  sand  until  it  weighs  an  even  number  of 
pounds. 

Attach  a  spring  balance  to  the  car.  Draw  the  car  along  the  table.  Does 
the  spring  balance  show  any  resistance  due  to  friction?  If  so,  this  must  be 
deducted  from  future  readings. 

Now  pull  the  loaded  car  up  the  inclined  plane.  How  does  the  acting 
force  compare  with  the  load? 

Support  the  plane  so  that  its  height  is  one  fourth  of  its  length.  Pull  the 
loaded  car  up  the  plane.  How  does  the  acting  force  compare  with  the 
load? 

Try  several  experiments,  varying  the  height  of  the  plane,  and  the  amount 
of  the  load.  Record  your  results  in  a  table,  as  follows: 


Height  of 
plane 

Length  of 
plane 

Ratio  of 
height  to  length 

A  cting 
force 

Load 

Ratio  of 
force  to  load 

'•;     • 

Conclusion: 
What  is  the  mechanical  advantage  of  an  inclined  plane? 

Questions: 

1.  Where  are  inclined  planes  used  in  your  house  and  about  the  grounds  ? 

2.  Where  else  have  you  seen  inclined  planes  in  use? 


PROBLEM  1 1 :  To  STUDY  A  WEDGE  —  THE  KNIFE-BLADE. 

Directions: 

Examine  the  blade  of  a  knife. 

Compare  its  two  edges.   How  does  the  thickness  of  the  dull  edge  com- 
pare with  the  width  of  the  blade? 

Lay  the  blade  flat  on  the  table. 

Does  it  resemble  any  other  machine  which  you  have  studied  ? 

Cut  a  piece  of  cheese  or  soft  wood. 

How  does  the  wedge  work? 

What  causes  the  resistance? 


WORK  WITH  EVERYDAY  MACHINES      315 

Questions: 

1.  How  does  a  wedge  resemble  an  inclined  plane  ? 

2.  Has  a  thin  or  a  thick  wedge  a  greater  mechanical  advantage? 

3.  Where  have  you  seen  wedges  used? 

Home  Work: 

How  many  kinds  of  wedges  can  you  find  in  your  home? 

PROBLEM  12:  To  STUDY  A  SCREW. 

Directions: 

Cut  a  right-angled  triangle  of  paper  four  inches  high  and  six  inches 
long. 

Holding  the  highest  part  close  to  a  pencil,  wind  the  triangle  around  the 
pencil. 

Compare  this  arrangement  with  a  common  screw.  In  what  ways  are 
they  alike? 

Call  the  ridge  running  spirally  around  the  screw  the  thread;  and  the 
distance  between  turns  of  the  thread  the  pitch  of  the  screw. 

Unwind  the  paper  triangle.     What  machine  does  a  screw  resemble? 

When  screws  are  used  in  wood,  what  causes  the  resistance?  Is  resist- 
ance useful  or  harmful  in  this  case? 

Questions: 

1.  How  does  a  screw  resemble  an  inclined  plane? 

2.  Is  it  easier  to  use  a  screw  of  fine  or  coarse  pitch?    Why? 

3.  What  other  machines  depend  upon  the  principle  of  the  screw? 

Home  Work: 

1.  Where  are  screws  used  in  your  house? 

2.  What  other  machines  depend  on  the  principle  of  the  screw? 

PROBLEM  13:  WHAT  ARE  THE  PARTS  OF  A  SEWING  MACHINE? 

Directions: 

What  is  the  make  of  your  machine? 

Find  the  following  parts: 

Treadle  Presser  foot 

Connecting  rod  Needle 

Wheel  below  table  Needle-plate 

Wheel  above  table  Feed 

Spool-holder  Bobbin 

Shaft  Bobbin-winder 

Needle-bar  Stitch-control 

Show  by  a  diagram  the  relation  of  the  parts. 

Question: 
Why  must  a  sewing  machine  be  oiled  frequently? 


THE  WORK  OF  THE  WORLD 


PROBLEM  14:  To  USE  A  SEWING  MACHINE. 

Directions: 

1.  Oil  the  machine.     How  many  oil  holes  do  you 
find?    What  is  the  reason  for  using  oil? 

2.  Clean  the  machine.     Use  a  soft  cloth.     Why 
should  the  machine  always  be  wiped  before  using? 

3.  What  is  the  relation  of   the  treadle  to  the 
connecting  rod?      What  does  the  connecting  rod 
do?     How  many  times  does  the  drive  wheel  turn 
around  for  one  forward  and  back  motion  of  the 
treadle?      Try    to     treadle     evenly    for    several 
minutes. 

4.  What   connects   the  wheel   below  the  table 
with  the  wheel  above?     Measure  the  diameter  of 
the    large   wheel.      What    is    its    circumference? 
Measure  the  diameter  of  the  small  wheel.     What 
is  its  circumference?     Provided  there  is  no  slip- 
ping of  the  belt,  how  many  times  will   the  small 
wheel  revolve  while  the  large  wheel  is  revolving 
once? 

5.  Make  a  mark  on  the  circumference  of  the 
small   wheel.       Turn    it    carefully   around    once, 
counting  the  number  of  stitches  made  by  the  nee- 
dle.    How  many  stitches  are  taken,  then,  to  each 
revolution  of  the  large  drive  wheel? 

6.  Place  a  heavy  piece  of  brown  paper  under  the 

presser  foot  and  stitch  for  one  minute.      Count  the  number  of  stitches. 
How   many  stitches  can  you 

make  in  one  minute?  With  a 
needle  and  thread  sew  a  piece  of 
cloth  one  minute,  using  back 
stitches  of  the  same  size  as  the 
machine  stitch.  How  many 
stitches  can  you  make?  How 
much  faster  can  you  sew  by 
machine  than  by  hand? 

7.  What  is  the   purpose  of 
the  presser  foot?     How  is  it 
raised  from  the  cloth? 

8.  Remove  the  face  plate  if 


S58T 


FIG.  157.  The  way  the 
stitches  are  formed  with 
a  double-thread  machine 
using  a  vibrating  shuttle. 

{Courtesy,  Singer  Sewing 
Machine  Co.) 


possible,  and  find  out  how  the 
rotary  motion  of  the  wheel 
produces  the  up  and  down 
motion  of  the  needle. 


FIG.  158.  A  single-thread  machine  which  forms 
a  chain  stitch  by  means  of  a  "looper"  under  the 
doth  plate. 

(Courtesy,  Singer  Sewing  Machine  Co.) 


WORK  WITH  EVERYDAY  MACHINES      317 

9.  How  is  the  length  of  the  stitch  regulated?  Does  the  length  of  the 
stitch  depend  on  the  speed  of  the  needle  or  the  motion  of  the  feed? 

10.  Thread  the  machine.     Is  a  bobbin  used?    Is  the  machine  a  chain- 
stitch  or  a  lock-stitch  machine? 

11.  Remove  the  needle  and  insert  it  again.      How  is  it  held  in  place? 

12.  Bring  samples  of  different  kinds  of  stitching  that  you  can  do:  such 
as 

Stitching  straight  on  striped  material. 
Stitching  straight  on  plain  material. 

PROBLEM  15:  WHAT  is  THE  USE  OF  A  PENDULUM  IN  A  CLOCK? 

Directions: 

1.  Make  a  pendulum  by  suspending  a  weight  by  a  thread  to  some  fixed 
support.     Pull  the  pendulum  to  one  side  and  let  it  go.     Explain  what 
happens.     Can  you  find  out  why  a  pendulum  clock  must  be  wound  up? 

2.  Find  out  whether  a  pendulum  clock  keeps  regular  time.     To  solve 
this  problem,  try  swinging  the  pendulum  a  very  short  distance,  count- 
ing the  number  of  trips  it  makes  in  one  minute.     Now  swing  it  a  much 
longer  distance,  and  count  the  trips  it  makes  in  one  minute.     How  do 
the  two  numbers  compare?    As  the  trips  made  by  the  pendulum  grow 
shorter,  should  the  clock  lose  time  or  gain  time? 

3.  Find  out  how  to  regulate  a  pendulum  clock.   To  solve  this  part  of 
the  problem,  use  a  pendulum  twenty  inches  long.     How  many  oscilla- 
tions (trips)  does  it  make  in  one  minute?    Shorten  the  pendulum  to  fif- 
teen  inches.     How  many  oscillations   does    it   make   in   one  minute? 
Shorten  it  again  to  ten  inches.     How  many  oscillations  does  it  make  in 
one  minute?    If    the  clock  is  gaining  time,  should   the  pendulum  be 
lengthened  or  shortened? 

Questions: 

1.  Does  a  pendulum  clock  keep  regular  time? 

2.  How  can  you  make  a  pendulum  clock  gain  or  lose  time? 

3.  What  forces  cause  a  pendulum  clock  to  keep  going? 

Necessary  work.  Most  of  the  machines  in  the  world  are  made 
for  the  purpose  of  getting  work  done.  Such  a  vast  amount  of 
work  must  be  done  every  day  that  the  unaided  strength  of  man 
cannot  accomplish  it  all.  Homes  must  be  built;  clothing  must  be 
made ;  fields  must  be  cultivated ;  food  must  be  harvested  and  sent 
to  all  parts  of  the  world.  In  your  home  the  meals  must  be  pre- 
pared, the  marketing  done,  the  dishes  washed,  the  house  kept 
clean  and  sanitary.  In  the  office  the  correspondence  must  be 
attended  to ;  orders  must  be  given  and  received ;  files  and  records 


3i8  THE  WORK  OF  THE  WORLD 

must  be  kept.  In  the  store,  goods  must  be  unpacked  and  put  in 
stock,  and  when  sold  they  must  be  packed  and  shipped,  and 
accurate  account  must  be  kept  of  all  money  received  and  spent. 
In  the  factory  the  raw  material  must  be  received,  unpacked, 
and  so  treated  as  to  be  made  into  the  finished  product,  and 
the  waste  material  must  be  utilized  for  side  prodijcts.  All  of 
these  processes  require  hosts  of  workers  and  thousands  of 
machines. 

Work  requires  energy.  You  know  that  you  cannot  always 
work  with  the  same  efficiency;  sometimes  you  have  more  en- 
ergy than  at  other  times.  A  man  who  has  been  lost  for  days  in 
a  mine  can  hardly  crawl  along.  He  has  had  no  food  to  give  him 
energy  enough  for  walking.  A  boy  who  is  recovering  from  a  fever 
cannot  run  and  shout  as  usual;  the  energy  in  his  body  is  being 
used  in  rebuilding  the  injured  cells.  The  girl  who  goes  back  to 
school  too  soon  after,  a  serious  illness  is  unwise ;  she  has  not  energy 
enough  to  do  efficient  work  and  to  get  well  at  the  same  time. 

If  we  inquire  into  what  this  mysterious  possession  is,  which  is 
so  necessary  for  our  efficiency,  we  can  only  say  that  energy  is  the 
capacity  for  doing  work.  (See  page  210.) 

Work  requires  force.  The  mere  possession  of  energy  does  not 
mean  that  the  possessor  is  accomplishing  any  work.  To  produce 
work  some  force  must  be  used.  A  force  is  a  push  or  a  pull  acting 
between  two  bodies  of  matter. 

If  a  boy  bats  a  ball,  the  bat  pushes  against  the  ball  and  the 
ball  pushes  against  the  bat.  Since  the  force  with  which  the  bat 
pushes  is  greater,  the  ball  is  sent  flying  through  the  air.  When  a 
fisherman  hauls  in  his  fish,  he  pulls  up  on  the  line  while  the  fish 
pulls  down.  If  the  force  of  his  pull  is  greater  than  the  force 
exerted  by  the  fish,  he  succeeds  in  his  work  of  getting  the  fish  from 
the  water. 

In  the  two  examples  mentioned  in  the  last  paragraph,  the 
forces  were  not  equal,  or  balanced.  One  force  was  greater  than 
the  other  in  each  case.  When  two  unbalanced  forces  act  on 
each  other,  motion  is  produced. 

You  can  think  of  many  cases  where  the  forces  are  balanced. 
A  team  of  horses  trying  to  draw  a  heavy  load  may  come  to  a 


WORK  WITH  EVERYDAY  MACHINES       319 


FIG.  159.  A  condition  of  stress,  due  to  balanced 
forces. 


stop  upon  a  hill.  The  force  which  they  exert  in  pulling  the  wagon 
is  balanced  by  the  downward  pull  of  the  load.  This  condition 
results  in  a  strain  or  stress,  but  not  in  the  accomplishment  of  work. 
Not  until  the  horses  are  able  to  exert  a  force  greater  than  the  pull 
of  the  load  is  any  move- 
ment of  the  wagon  pro- 
duced. 

Work  results  in  motion. 
Time  and  effort  are  not 
counted  in  measuring 
work ;  only  accomplish- 
ment counts.  A  man 
may  use  much  energy  in 
pushing  for  hours  in  an 
effort  to  move  a  heavy 
automobile,  but  unless  he 
actually  moves  it,  he 

accomplishes  no  work.      Work  is  sometimes  defined  as  a  "  push 
or  a  pull  acting  through  distance." 

Work  does  not  mean  drudgery.  If  a  boy  bats  his  ball,  jumps 
on  his  sled,  turns  a  somersault,  or  climbs  a  tree,  he  is  doing  work. 
He  possesses  energy;  he  uses  force;  he  produces  motion.  These 
are  the  three  requirements  for  accomplishing  mechanical  work. 

Resistance  to  work.  The  reason  that  work  is  often  hard  to  per- 
form is  because  the  force  applied  usually  meets  with  resistance. 
In  doing  mechanical  work  we  meet  with  three  causes  for  resist- 
ance :  weight,  friction,  and  inertia. 

Weight.  You  have  found  that  you  can  lift  certain  things 
very  easily;  others  you  cannot  move  at  all.  In  some  cases  your 
muscular  force  can  more  than  balance  the  force  pulling  down 
on  the  objects  you  are  lifting;  in  the  other  cases  the  downward 
pull  is  much  greater  than  any  force  you  are  able  to  exert.  Weight 
is  a  measure  of  the  force  of  gravity,  or  the  downward  pull  of  the 
earth.  We  measure  the  force  of  gravity  in  pounds  and  ounces. 
If  you  weigh  ninety-five  pounds,  it  is  because  the  earth  is  pull- 
ing you  toward  itself  with  the  same  force  that  it  would  pull  other 
weights  amounting  to  ninety-five  pounds. 


320 


THE  WORK  OF  THE  WORLD 


When  you  try  to  move  anything,  you  must  reckon  on  this 
force  of  gravity.  If  you  lift  an  object,  you  are  working  against 
the  force  of  gravity,  and  can  only  accomplish  results  if  your 
force  is  greater  than  the  weight  of  the  object. 

Friction.  If  you  try  to  push  a  piano  across  the  room  you  meet 
with  resistance,  due  not  only  to  the  weight  of  the  piano,  but  due 
also  to  the  friction.  Friction  is  the  resistance  which  opposes  an 
effort  to  slide  or  roll  one  surface  over  another.  Every  surface  is  more 
or  less  rough.  The  rough  places  on  one  surface  catch  upon  the 

rough  places  on  the  other,  and 
cause  friction.  Friction  varies 
with  the  smoothness  of  the  sur- 
face. 

You  can  coast  downhill  on  the 
snow  and  ice  with  breath-taking 
speed,  but  you  would  never 
think  of  trying  your  sled  on  the 
same  hill  in  summer.  The  fric- 
tion be'tween  the  runners  and  the 
ground  is  much  greater  than  the 
friction  between  the  runners  and 
the  snow. 

Perhaps    you   have  a  coaster 
for  summer  use.    It  has  wheels 
instead  of  runners,  because  roll- 
ing friction  is  less  tlian  sliding  friction.      The  ball  bearings  in 
your  bicycle  and  in  an  automobile  make  use  of  this  principle, 
as  do  the  wheels  of  all  vehicles. 

Friction  is  a  hindrance  to  some  of  our  work,  but  a  help  to  us  in 
many  other  ways.  You  know  how  hard  it  is  to  run  or  walk  on 
ice.  This  is  because  there  is  very  little  friction  between  leather 
and  ice.  Without  friction  between  shoe  leather  and  the  pave- 
ment we  could  not  walk  or  run;  without  friction  between  tires 
and  roads  our  automobiles  and  carriages  could  not  move ;  without 
friction  between  the  wheels  and  the  steel  tracks  electric  cars  and 
steam  trains  would  stand  still ;  without  the  friction  between  wood 
and  steel  buildings  would  fall  apart  because  the  nails,  screws,  and 
bolts  would  not  be  held  in  place. 


FIG.  160.  Ball  bearings. 
(Courtesy,  New  Departure  Mfg.  Co.) 


WORK  WITH  EVERYDAY  MACHINES      321 


Inertia.  When  you  tried  the  experiment  with  the  coin  (see 
page  308),  perhaps  you  were  surprised  that  it  failed  to  move  with 
the  card.  It  was  because  of  the  inertia  of  the  coin.  The  resist- 
ance due  to  inertia  can  be  seen  everywhere.  The  law  of  inertia 
is :  A  body  at  rest  tends  to  remain  at  rest,  and  a  body  in  motion  tends 
to  remain  in  the  same  motion,  unless  acted  on  by  some  outside  force. 

If  you  have  ever  been  "  stalled  "  in. an  automobile  you  realize 
how  a  body  at  rest  tends  to  remain  at  rest.  It  requires  a  strong 
push  from  outside,  or  the  force  of  the  starting  motor,  to  move 
the  car.  The  explanation 
is  of  course  that  gravity 
is  operating  all  the  time, 
holding  the  car  in  place 
with  a  force  equal  to  its 
weight. 

The  force  that  the  man 
at  bat  applies  to  the  base- 
ball would  send  the  ball 
on  and  on,  if  it  were  not 
for  the  friction  of  the  air 
and  the  force  of  gravity. 

The    principle  of   iner- 
tia, while  a  hindrance  to 
the  working  of  some  ma- 
chines,   is   a   help   in   other    cases.      The   centrifugal   washing 
machine,  the  salt  evaporating  machine,  and  the  cream  separator 
depend  upon  it  to  accomplish  their  work. 

How  work  is  measured.  If  you  lift  a  two-pound  package  of 
sugar  to  a  shelf  two  feet  high,  you  are  accomplishing  a  certain 
amount  of  work.  If  you  were  to  lift  it  higher  you  would  be  doing 
more  work.  If  the  package  were  heavier  you  would  also  be  doing 
more  work.  In  measuring  work  we  must  therefore  take  into  con- 
sideration the  force  which  is  exerted,  and  the  distance  the  body 
is  moved.  Scientists  call  the  unit  used  in  measuring  work  a  foot 
pound.  When  a  pull  equal  to  the  earth's  pull  on  a  pound  of 
matter  acts  through  a  foot  of  space,  the  work  done  is  one  foot 
pound.  In  lifting  your  two  pound  package  two  feet,  you  would 


FIG.  161.  One  foot  pound  of  work. 


322 


THE  WORK  OF  THE  WORLD 


do  four  foot  pounds  of  work.  In  lifting  it  four  feet  you  would 
do  eight  foot  pounds.  This  rule  may  be  expressed:  work  equals 
weight  times  distance.  Why  is  it  easier  to  hang  clothes  if  the 
clothes-basket  is  first  placed  on  a  stool? 

Simple  machines.     A  machine  is  a  device  which  lightens  the 
labor  of  man  or  gives  him  more  efficiency  in 
his  work. 

The  types  of  machines  in  use  to-day  are 
too  many  to  be  thoroughly  understood  by 
any  one  man  in  a  lifetime.  We  can,  how- 
ever, very  easily  understand  the  principle 
on  which  they  depend,  for  nearly  every 
machine,  no  matter  how  complicated,  con- 
sists of  combinations  and  variations  of  just 
two  simple  machines,  the  lever  and  the  in- 
clined plane. 

The  lever.     Probably  it  was  very  early 


t 


FIG.  162.  A  diagram  of  the  equal-arm  balance.  The 
pans  of  this  balance  are  carried  on  the  knife  edges 
(the  triangles  shown  at  the  bearing  poi-nts  under  the 
pans,  at  equal  distances  from  the  center  of  fulcrum 
knife  edge).  The  scale  comes  to  balance  when  the 
weights  on  the  two  pans  are  equal.  The  load  to  be 
weighed  is  placed  on  one  pan  and  known  weights  are 
added  to  the  other  until  the  scale  is  in  balance.  The 
correct  name  for  this  type  is  "the  equal-arm  stabil- 
ized scale." 

(Courtesy,  U.S.  Bureau  of  Standards.) 


FIG.  163.  A  diagram  of  the 
spring  balance.  The  load 
placed  on  the  pan  P  stretches 
the  two  springs  S,  S.  The 
motion  of  the  cross  bar 
below  the  springs  is  trans- 
mitted through  the  vertical 
toothed  bar  or  rack  R  turning 
the  small  gear  G,  mounted 
on  a  spindle  bearing  the 
pointer  /.  The  pointer  ro- 
tates over  the  dial,  a  portion 
of  which  with  the  pointer  is 
shown  in  dotted  outline. 

(Courtesy,  U.S.  Bureau  of 
Standards.) 


in  the  history  of  the  human  race  that  some  savage,  brighter 
than  his  fellows,  discovered  that  with  the  aid  of  a  long  stick  he 
could  move  a  weight  that  was  too  much  for  his  unaided  strength. 
That  was  the  first  lever.  The  muscular  force  with  which  the 
savage  pushed  down  upon  the  long  end  of  his  stick  we  may  call 


WORK  WITH  EVERYDAY  MACHINES      323 


t   T 


the  acting  force  ;  the  weight  of  the  great  stone  was  the  resistance; 
and  the  small  stone  or  ridge  against  which  he  rested  his  lever  we 
may  call  the  fulcrum. 

You  have  found  from  your  problems  that  a  lever  is  a  rod  free 
to  turn  about  a  point.  This  point  is  always  called  the  fulcrum; 
the  two  opposing  forces 
are  the  acting  force  and 
the  resisting  force.  It  is 
plain  that  when  these  two 
forces  are  exactly  equal, 
their  distances  from  the 
fulcrum  must  be  exactly 
the  same  if  they  are  to 
balance. 

On  this  principle  de- 
pends the  common  scales 
or  balances.  The  object 
to  be  weighed  is  placed 
on  one  pan,  the  weights 
upon  the  other  pan.  The 
force  of  gravity  tends  to 
pull  them  both  down,  but 
is  prevented  because  of 
the  upward  pressure  at 
the  balancing  point,  or 
fulcrum.  If  the  two  forces 
are  not  exactly  equal,  one 
side  or  the  other  tips 
down  towards  the  earth. 

The  balance  in  the  dia- 
gram has  arms  of  equal  length.  Many  levers,  however,  are 
made  with  unequal  arms.  If  the  arms  are  unequal,  the  acting 
force  and  the  resistance  are  unequal.  A  small  force  acting 
on  a  long  arm  can  balance  a  much  larger  resistance  acting  on  a 
short  arm. 

The  law  of  the  lever  is  expressed  thus :  The  force  times  the  force 
arm  equals  the  resistance  times  the  resistance  arm. 


0 


FIG.  164.  Levers  of  the  first  type.  P,  power  or 
acting  force;  w,  weight  or  resistance;  /,  fulcrum  or 
turning  point. 


324 


THE  WORK  OF  THE  WORLD 


f 


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z&*~fr.-:&-:$j 

asss^r^v?^ 

<J> 


Every  lever  has  a  force  arm  and  a  resistance  arm.  Different 
arrangements  make  possible  three  types  of  levers : 

/.  Levers  of  the  first  type.  A  first  type  lever  has  the  fulcrum  be- 
tween the  acting  force  and  the  resistance.  In  our  homes  are 
many  levers  of  this  type.  A  coal  shovel  is  held  so  that  the  ful- 
crum, or  turning  point,  is  part  way  up  the  shaft.  The  weight  of 

the  coal  is  the  resistance, 
and  the  muscular  force 
pushing  down  on  the 
handle  the  acting  force. 
A  pair  of  scissors 
makes  use  of  two  rods 
free  to  turn  about  a 
point.  Much  greater 
force  is  necessary  to  cut 
wire  than  to  cut  cloth; 
therefore  wire  cutting 
pliers  have  a  much 
shorter  resistance  arm 
and  a  longer  force  arm 
than  ordinary  shears. 

In  a  first  type  lever 
the  acting  force  may  be 
either  greater  or  smaller 
than  the  resistance. 

2.  Levers  of  the  second 
type.  A  second  type 
lever  has  the  resistance 
between  the  fulcrum  and 
the  acting  force.  Since 
the  acting  force  has  the 
longer  arm,  the  force  is  always  smaller  than  the  resistance. 

A  common  example  is  a  wheelbarrow,  where  the  force  ap- 
plied at  the  handles  need  not  be  so  great  as  the  weight  of  the 
load. 

3.  Levers  of  the  third  type.  When  the  acting  force  is  applied  be- 
tween the  fulcrum  and  the  resistance,  the  lever  is  of  the  third 


FIG.  165.  Levers  of  the  second  type.  Explain  the 
arrangement  of  acting  force,  resistance,  and  fulcrum 
in  each  case. 


WORK  WITH  EVERYDAY  MACHINES      325 


type.  Now  the  force  arm  is  the  shorter,  therefore  the  acting  force 
is  greater  than  the  resistance. 

Such  a  lever  is  used  when  it  is  desirable  to  move  a  light  body 
rapidly  a  long  distance,  as  in  a  merry-go-round.  A  common 
household  example  is  a  pair  of  fire-tongs. 

The  mechanical  advantages  of  levers.  No  machine  can  do  any 
work  by  itself;  it  can  only  transmit  the  work  put  into  it.  This 
statement  may  sound 
startling  to  you  when 
you  consider  what  it 
means.  Perhaps  you 
have  seen  a  man,  with 
the  aid  of  a  long  crow- 
bar, pry  up  a  boulder 
much  larger  than  him- 
self. Can  it  be  that  the 
machine  did  no  more 
work  than  the  man? 

Let  us  see.  The  crow- 
bar is  a  lever.  Every 
lever  has  its  fulcrum, 
its  force  arm,  and  its 
resistance  arm.  If  the 
fulcrum  is  very  near  the 
boulder,  the  resistance 
arm  may  be  only  3 
inches  long.  If  the  force 
arm  is  5  feet  long,  it  is 
20  times  the  length  of 
the  resistance  arm.  Then 
a  man  exerting  a  force 

of  150  pounds  can  support  a  boulder  weighing  3000  pounds. 
Since  there  is  some  friction  in  the  machine,  and  the  inertia  of  a 
body  at  rest  must  be  overcome,  it  actually  takes  a  force  some- 
what greater  than  150  pounds  to  lift  a  3OOO-pound  weight  with 
this  type  of  machine. 

One  advantage  of  a  lever  is,  therefore,  that  by  using  arms  of 


FIG.  166.  Levers  of  the  third  type.  Explain  each  case. 


326  THE  WORK  OF  THE  WORLD 

very  different  length,  a  small  force  is  able  to  overcome  a  large 
resistance. 

If  you  have  ever  ridden  on  a  see-saw  with  a  person  much 
heavier  than  yourself,  you  have  seen  another  advantage  of  a 
lever.  A  man  sits  close  to  the  fulcrum,  and  "  works  "  the  see-saw. 
His  weight  is  the  acting  force;  the  child's  weight  the  resistance. 
If  he  is  3  feet  from  the  fulcrum,  and  weighs  150  pounds,  he  can 
balance  a  child  who  weighs  75  pounds  and  sits  6  feet  from  the 
fulcrum.  The  fun  of  it,  for  the  child,  lies  in  the  fact  that  he 
travels  much  faster  and  farther  than  the  man. 

Two  advantages  of  levers  are  thus  seen  to  be  that  a  small  force 
is  able  to  overcome  a  large  resistance,  and  that  a  light  body  can  be 
moved  rapidly  over  a  long  distance. 

The  efficiency  of  a  machine.  If  the  man  on  his  see-saw  moves 
I  foot,  he  is  doing  150  foot  pounds  of  work.  His  machine,  the 
see-saw,  cannot  do  more  than  150  foot  pounds,  or  move  its  75- 
pound  weight  more  than  2  feet. 

The  i5O-pound  man  with  the  crowbar  pushes  down  his  end  of 
the  bar  3  feet.  He  does  3  X  150  or  450  foot  pounds  of  work.  His 
machine  if  100  per  cent  efficient  would  lift  3000  pounds,  but  it 
could  do  only  the  same  amount  of  work  the  man  does,  450  foot 
pounds.  It  could  only  lift  the  boulder,  therefore  .15  of  a  foot, 
not  quite  2  inches. 

The  work  done  by  a  machine  cannot  be  greater  than  the  work 
put  into  a  machine.  If  a  machine  without  friction  could  be 
made,  the  amount  of  work  done  by  a  machine  would  be  exactly 
equal  to  the  amount  of  work  put  in.  Since  it  is  impossible  to 
make  a  frictionless  machine,  the  efficiency  of  a  machine  is  meas- 
ured by  the  comparison  between  the  work  put  in  and  the  work 
done  by  the  machine.  It  is  usually  expressed  in  percentage. 

useful  work  out 

Efficiency  = — — 

total  work  in 

A  modified  lever  —  the  crank  and  axle.  Many  books  state 
that  the  simple  machines  are  six  in  number,  the  lever,  the  crank 
and  axle,  the  pulley,  the  inclined  plane,  the  wedge,  and  the  screw. 
If  we  reduce  them  to  their  very  lowest  terms,  however,  we  find 


WORK  WITH  EVERYDAY  MACHINES      327 

that  the  first  three  are  all  forms  of  levers,   and  the  last  three 
forms  of  inclined  planes. 

The  bread-mixer  is  made  with  a  crank  and  axle.  It  is  plainly 
seen  to  be  really  a  lever,  the  fulcrum  being  over  the  center  of  the 
pail,  at  the  end  of  the  crank,  the  acting  force  being  at  the  other 
end  of  the  crank,  and  the  resistance  being  applied  between,  where 
the  curved  metal  strikes  the  dough.  What  type  of  lever  is  this? 
Crank  and  axle  or  wheel  and  axle  machines 
are  abundant.  Study  the  illustrations. 

Another  modified  lever  —  the  pulley.    Ar- 
chimedes was  a  great  inventor  who  lived  over 


FIG.  167.  A  drill,  a 
machine  tool  which 
has  a  wheel  and  axle 
and  gear  wheels. 

(Courtesy,  Goodell- 
Pratt  Co.) 


FIG.  168.  Gears  in  an  automobile.  The  gear 
principle  depends  on  the  law  of  the  lever.  The  act- 
ing force  is  applied  at  the  circumference  of  the  gear 
wheel.  The  larger  the  wheel,  the  longer  is  the  force 
arm. 

(Courtesy,  New  Departure  Mfg.  Co.) 


two  thousand  years  ago,  in  the  Greek  city  of  Syracuse.  One 
day  he  told  his  king  that  with  his  own  strength  he  could  move 
any  weight  whatever.  The  king  was  naturally  doubtful,  so 
Archimedes  ordered  that  one  of  the  king's  galleys  should  be 
drawn  up  on  the  shore.  By  hard  tugging  of  many  slaves  this 
was  done.  Then  Archimedes,  watched  by  the  whole  court,  moved 
with  his  hand  the  end  of  a  machine  which  consisted  of  a  num- 
ber of  ropes  and  pulleys.  Easily  and  gently  the  great  ship 
moved  over  the  sand.  Can  you  picture  the  astonishment  of  the 
king  and  his  court? 


328  THE  WORK  OF  THE  WORLD 

If  you  have  tried  the  problem  on  pulleys  you  have  found  that 
a  fixed  pulley  has  only  one  advantage,  to  change  the  direction  in 
which  the  acting  force  is  applied.  It  is  a  very  simple  modifica- 
tion of  a  lever  of  the  first  type.  (See  figure  154.) 

A  movable  pulley  has  another  advantage,  however.  This  is 
a  lever  of  the  second  type.  Since  the  force  arm  is  just  twice  as 
long  as  the  resistance  arm,  the  acting  force  needs  to  be  only  half 
as  great  as  the  weight  to  be  lifted.  (See  figure  155.) 

When  several  pulleys  are  arranged  together  in  a  block  and 
tackle,  the  advantages  of  the  fixed  and  movable  pulleys  are  com- 
bined. Suppose  a  block  of  4  movable  pulleys  is  used  to  raise  a 
piano  weighing  800  pounds.  It  is  evident  that  8  strands  of  rope 
are  used  to  support  the  block  which  lifts  the  piano.  Each  strand 
supports  only  one  eighth  of  the  weight  of  the  piano.  The  fixed 
pulleys  are  used  only  to  change  the  direction  of  the  force.  If  we 
could  disregard  friction,  a  pull  of  100  pounds  on  the  rope  would 
be  enough  to  support  the  piano.  Since  there  is  some  friction, 
and  since  the  inertia  of  a  body  at  rest  must  be  overcome,  the  force 
of  somewhat  more  than  100  pounds  must  be  exerted  actually  to 

lift  the  piano.  The  me- 
chaniod  advantage  of  a 
machine  of  this  sort  is 
sometimes  said  to  be  8. 
What  is  the  mechanical 
advantage  of  the  sys- 
tem of  pulleys  shown  in 
figure  156? 
The  inclined  plane. 

FIG.  169.  An  inclined  plane. 

You    have    often   seen 

workmen  rolling  heavy  barrels  up  into  wagons.  The  machine 
they  used  was  an  inclined  plane.  The  advantage  of  the  inclined 
plane  is  that  a  small  force  by  acting  through  a  long  distance, 
can  raise  a  weight  which  it  cannot  lift  vertically.  It  would 
be  impossible  for  you,  for  example,  to  lift  a  trunk  which 
weighed  two  hundred  pounds  into  a  wagon  which  was  two  feet 
above  the  ground.  But  by  the  use  of  a  board  eight  feet  long, 
with  a  roller  to  reduce  friction,  you  could  push  the  trunk 


WORK  WITH  EVERYDAY  MACHINES      329 


into  the  wagon  by  expending  the  force  of  but  little  more  than 
fifty  pounds. 

The  law  of  the  inclined  plane  may  be  expressed  thus:  the  act- 
ing force  times  the  dis- 
tance it  moves  equals  the 
resistance  times  the  dis- 
tance it  moves. 

A    modified    inclined 
plane  —  the  wedge.   Ev- 
ery time  you  use  your 
knife-blade,    and    every 
time    you    chop    wood 
with    an   axe,    you   are 
using  a  machine,  a  kind 
of  inclined  plane.     The 
shape   of   these    instru- 
ments      clearly       shows  FIG.  170.  One  use  of  a  wedge, 
their   relationship.     In- 
stead of  lifting  a  weight,  however,  in  these  cases  you  are  forc- 
ing your  machine  itself  into  the  wood,  or  the  food,  and  overcom- 
ing the  resistance  offered  by  the  particles  as  they  cling  together. 

The  first  wedges  known  were  the 
teeth  of  animals  and  men.  The 
front  teeth,  used  for  biting,  are 
wedges. 

The  screw  —  an  inclined  plane. 
Some  kinds  of  desk  chairs  are 
raised  and  lowered  by  means  of 
screws.  A  vise  such  as  is  used 
in  the  carpenter  shop  is  another 
example  of  a  screw.  If  you  cut 
a  paper  triangle  and  wind  it  around 
a  pencil,  you  can  see  the  relation- 
ship between  a  screw  and  an  in- 
clined plane.  The  finer  the  pitch  of  the  screw  (see  problem  12)  the 
less  force  required  to  make  one  turn;  just  as  in  the  inclined  plane, 
the  less  the  slope,  the  less  the  force  required  to  raise  a  body. 


FIG.  171.  A  vise,  which  depends  upon 
the  principle  of  a  screw. 

(Courtesy,  Goodell-Pratt  Co.) 


330  THE  WORK  OF  THE  WORLD 

The  efficiency  of  a  screw  is  small  because  the  friction  is  very 
large  in  proportion  to  the  force  applied.  In  fact,  it  is  the  friction 
which  makes  screws  useful  in  holding  boards  together 

A  great  inventor,  Galileo.  During  the  so-called  "  Dark  Ages,"  from 
about  600  A.D.  to  about  1500,  no  interest  in  inventions  was  shown.  Instead 
of  looking  to  nature  for  answers  to  their  problems,  men  turned  to  the  writ- 
ings of  ancient  philosophers.  They  seemed  afraid  to  think  for  themselves. 
In  contrast  to  these  timid  thinkers  stood  Galileo,  the  first  of  the  great  mod- 
ern scientists.  Even  as  a  boy  he  chose  to  think  for  himself.  Making  use 
of  his  knowledge  of  levers  and  inclined  planes,  he  loved  to  form  mechanical 
toys,  which,  although  they  did  not  always  work,  won  him  great  admiration 
among  his  boy  companions.  His  father,  however,  a  famous  musician  of 
the  time,  did  not  share  the  boys'  admiration  for  his  son's  mechanical 
bent,  and  insisted  on  sending  him  to  the  University  of  Pisa  to  study 
medicine. 

The  invention  of  the  pendulum  clock.  While  Galileo  was  at  the  Univer- 
sity of  Pisa,  where  he  sadly  neglected  his  medical  studies,  he  discovered 
something  which  has  made  possible  all  our  clocks  run  by  pendulums.  One 
day  when  he  was  in  the  cathedral,  his  attention  wandered  from  his  prayers 
to  a  great  bronze  lamp  which  hung  from  the  ceiling.  Some  one  had  drawn 
it  aside  to  light  it,  and  when  it  was  released  it  swung  back  and  forth,  as 
hanging  lamps  and  pendulums  will  do.  Galileo,  curious  enough  to  time  its 
swinging  by  means  of  his  pulse,  made  the  startling  discovery  that  although 
the  length  of  the  swing  grew  smaller  and  smaller  as  the  lamp  gradually 
came  to  rest,  yet  the  time  of  each  swing  remained  the  same.  He  imme- 
diately set  to  work  to  use  this  idea  in  an  instrument  by  which  physicians 
might  count  the  pulse. 

Not  until  fifty  years  had  passed,  and  Galileo  was  an  old  man,  did  he  use 
the  same  idea  in  making  a  clock.  Then  by  means  of  a  pendulum,  some 
levers,  and  a  simple  system  of  cog-wheels,  he  invented  the  first  pendulum 
clock.  It  had  only  one  hand,  to  be  sure,  but  it  kept  regular  time,  and  was 
such  an  improvement  on  anything  then  in  use  that  it  marks  an  important 
epoch  in  invention. 

The  movement  to  and  fro  of  a  pendulum  depends  upon  (i)  the 
attraction  of  gravity,  which  pulls  it  down  from  the  raised  posi- 
tion; (2)  the  law  of  inertia,  which  makes  it  continue  its  swing 
until  the  forces  balance.  A  pendulum  gradually  comes  to  rest 
because  of  the  friction  with  the  air. 

Although  the  width  of  the  vibration  may  vary,  the  time  of  the 
vibration  is  the  same,  for  any  one  pendulum.  Pendulums  of 


WORK  WITH  EVERYDAY  MACHINES       331 

different  lengths  vibrate  at  different  rates;  the  shorter  the  pendu- 
lum, the  faster  it  vibrates. 

In  a  clock  the  movement  of  the  wheels  and  hands  depends  upon 
the  swinging  of   the   pen- 
dulum.    It  is  the  pendu- 
lum  that   really  measures 
off  the  time. 

Complex  machines.  We 
have  studied  six  simple 
machines,  which  can  all  be 
seen  to  depend  on  two 
principles.  The  machin- 
ery in  your  house  and  com- 
munity is  made  by  us- 
ing combinations  of  simple 
machines.  The  sewing  ma- 
chine, the  phonograph,  the 
washing  machine,  the  bi- 
cycle, and  the  automobile 
are  a  few  of  the  complex  machines  in  use.  Study  them  to  find 
what  kinds  of  simple  machines  they  contain,  and  how  they  are 
useful  in  helping  accomplish  work. 

INDIVIDUAL  PROJECTS 

Working  projects: 

1.  With  "Erector"  or  "Mechano"  construct  a  model  of  a  machine,  such  as 
a  balance,  a  derrick,  etc. 

2.  Demonstrate  how  a  spring  balance  works. 

3.  Demonstrate  the  mechanism  of  a  complex  machine,  such  as: 

(1)  A  clothes- wringer. 

(2)  A  phonograph. 

(3)  A  dish-washing  machine. 

(4)  A  clock. 

(5)  A  sewing  machine. 

Reports: 

Several  interesting  subjects  are  mentioned  in  the  list  of  references.    What 
others  can  you  suggest? 


FIG.  172.  What  kinds  of  simple  machines  can  you 
find  in  this  machine  tool? 

(Courtesy,  Gooddl-Pratt  Co.) 


BOOKS  THAT  WILL  HELP  YOU 

American  Book  Co. 


Great  Inventors  and  their  Inventions.     F.  P.  Bachman. 
Elias  Howe  and  the  Sewing  Machine. 
Cyrus  McCormick  and  the  Reaper. 
Henry  Bessemer  and  Steel. 


332  THE  WORK  OF  THE  WORLD 

Great  Inventions  and  Discoveries.     W.  D.  Piercy.    C.  E.  Merrill  Co. 
Harpers'  Machinery  Book  for  Boys.     J.  H.  Adams.     Harper  &  Bros. 

Sun-power,  wind-power,  and  water-power. 
Physics  of  the  Household.     C.  J.  Lynde.     The  Macmillan  Co. 
Mechanics  of  Sewing  Machines.     Singer  Sewing  Machine  Co. 
Stories  of  Useful  Inventions.     S.  E.  Forman.     Century  Co. 

A  history  of  inventions  useful  to  man  in  his  daily  life. 

The  Story  of  Agriculture  in  the  United  States.     A.  H.  Sanford.     D.  C.  Heath  & 
Co. 

The  Age  of  Machinery. 
The  Story  of  Iron  and  Steel.     J.  R.  Smith.     D.  Appleton  &  Co. 


PROJECT  XVI 
COMMUNICATION 

Importance  of  communication  to  our  civilization.  Living  in  a 
time  when  we  are  in  close  touch  with  practically  all  parts  of  the 
world,  we  find  it  difficult  to  imagine  that  in  the  past  people  were 
either  unable  to  communicate  with  each  other  or  did  so  with 
great  difficulty,  if  they  lived  very  far  apart.  It  was  not  much 
over  fifty  years  ago  that  news  from  Europe  took  three  or  four 
weeks  to  reach  us.  Can  you  imagine  what  it  would  be  like  to 
receive  news  from  Europe  several  weeks  after  the  events  reported 
had  occurred?  Yet  our  great-grandparents  had  to  be  satisfied 
with  that  condition. 

If  we  go  back  far  enough  in  the  history  of  mankind,  we  find 
that  at  one  time  people  lived  in  very  small  groups  and  had  no 
means  of  communicating  with  each  other  except  by  travel.  As 
people  in  those  days  did  not  travel  very  much,  they  usually  knew 
very  little  about  what  was  happening  in  any  other  places  outside 
of  their  own  little  communities^  Later,  as  men  learned  how  to 
live  in  larger  groups  it  became  increasingly  necessary  to  be  able 
to  carry  on  intercourse  with  people  living  in  other  parts  of  the 
world.  To-day  by  means  of  the  telephone,  the  telegraph,  sub- 
marine cables,  wireless  stations,  printing  presses  and  railroads 
even  the  smallest  community  can  usually  very  quickly  get  news 
about  events  that  may  be  happening  thousands  of  miles  away. 
In  this  project  we  shall  find,  out  how  these  modern  methods  of 
communication  have  been  made  possible. 

PROBLEMS 
PROBLEM  i :  WHAT  is  MEANT  BY  MAGNETIC  ATTRACTION? 

Directions: 

Touch  a  nail  to  one  of  the  poles  of  a  bar  magnet  or  horseshoe  magnet. 
While  the  nail  is  clinging  to  the  magnet,  touch  a  tack  to  the  end  of  the 
nail.  While  the  tack  is  held  to  the  nail,  dip  the  tack  into  some  iron  filings. 


334  THE  WORK  OF  THE  WORLD 

What  happens?     How  do  you  explain  the  fact  that  these  different  mate- 
rials will  hold  together? 

Detach  the  nail  from  the  magnet.  What  happens?  How  do  you  account 
for  this? 

PROBLEM  2:  WTHAT  is  THE  DIFFERENCE  BETWEEN  A  TEMPORARY  AND  A 
PERMANENT  MAGNET? 

Directions: 

Find  out  whether  your  knife-blade  is  a  magnet.  How  will  you  do  this? 
If  it  is  not  a  magnet,  see  if  you  can  make  it  one  by  rubbing  it  several  times 
along  a  bar  magnet  from  the  center  to  one  of  the  ends.  Now  see  whether 
it  has  become  magnetized.  If  it  has  not,  continue  to  rub  as  already  di- 
rected and  test  it  again.  What  is  the  result?  What  has  the  knife-blade 
become? 

Rub  a  nail  along  a  magnet  in  a  similar  manner  and  try  to  pick  up  a  tack 
with  it.  Do  you  know  the  difference  in  the  nature  of  the  iron  in  the  knife- 
blade  and  the  iron  nail  that  makes  them  behave  differently?  Which  can 
be  made  a  permanent  and  which  a  temporary  magnet? 

PROBLEM  3:  WHICH  MAGNETIC  POLES  ATTRACT  AND  WHICH  REPEL  EACH 
OTHER? 

Directions: 

Place  two  bar  magnets  with  their  north  poles  adjacent.  Do  they  tend 
to  cling  together? 

Place  two  bar  magnets  with  their  south  poles  adjacent.  Do  they  tend 
to  cling  together? 

Place  two  bar  magnets  with  their  unlike  poles  together,  one  north  and 
the  other  south  pole  touching.  Try  to  separate  them.  Do  they  stick 
together?  Try  the  opposite  unlike  poles.  What  is  the  result? 

Try  the  same  experiment  with  other  magnets.     What  are  the  results? 

Place  a  compass  needle  near  the  north  pole  of  a  bar  magnet.  What  is 
the  result? 

Place  the  compass  needle  near  the  south  pole.     What  is  the  result? 

Conclusion: 
Which  poles  attract  each  other  and  which  poles  repel? 

PROBLEM  4:  To  STUDY  THE  LINES  OF  FORCE  ABOUT  A  MAGNET. 
Directions: 

1.  Place  a  single  bar  magnet  under  a  thin  piece  of  cardboard.     Sprinkle 
iron  filings  on  this  paper  immediately  above  the  magnet  and  gently  tap     , 
the  paper.     Make  a  drawing  to  indicate  the  arrangement  of  the  filings. 

2.  Place  two  bar  magnets  similarly  under  paper  with  their  like  poles 


COMMUNICATION  335 

near  each  other.    Again  tap  the  paper  and  notice  the  manner  in  which  the 
filings  arrange  themselves.     Draw. 

3.  Again  follow  the  same  general  directions,  but  this  time  place  the 
unlike  poles  near  each  other.  Draw. 

Questions: 

1.  What  do  you  call  the  force  which  makes  the  iron  filings  arrange  them- 
selves in  a  definite  manner? 

2.  What  does  each  little  iron  filing  become  when  under  the  influence  of 
the  magnet? 

3.  What  do  the  lines  of  force  indicate  when  unlike  poles  are  placed  near 
each  other?   when  like  poles  are  close  together? 

PROBLEM  5 :  To  OBSERVE  WHETHER  THERE  ARE  ANY  LINES  OF  FORCE  ABOUT 

A- WIRE  CARRYING  AN  ELECTRIC  CURRENT. 

Directions: 

Place  a  compass  near  a  wire  carrying  an  electric  current.  Is  the  compass 
affected  in  a  noticeable  manner?  Reverse  the  direction  of  flow  of  the 
current  and  note  whether  the  compass  is  affected  in  the  same  manner  as 
before.  If  it  is  affected  differently,  can  you  observe  wherein  the  difference 
lies? 

Question: 
What  does  this  experiment  indicate  regarding  an  electric  wire? 

PROBLEM  6:  To  MAKE  AN  ELECTRO-MAGNET. 

Directions: 

Wrap  an  insulated  wire  about  a  small  bar  of  soft  iron  —  such  as  a  nail. 
Cause  an  electric  current  to  flow  through  the  wire.  Hold  small  tacks  near 
the  end  of  the  piece  of  iron.  What  properties  are  shown  by  the  iron  when 
the  electric  current  is  flowing?  Shut  off  the  current.  What  is  the  result? 
Is  the  iron  bar  any  longer  a  magnet? 

Determine  which  is  the  north  and  which  is  the  south  pole  of  the  iron 
piece  by  alternately  touching  its  ends  with  the  ends  of  a  bar  magnet  while 
the  current  is  flowing  through  the  wire.  Reverse  the  direction  of  flow 
of  the  current  and  perform  the  same  experiment.  What  is  the  result? 

PROBLEM  7:  WHAT  MAKES  AN  ELECTRIC  BELL  RING? 

Directions: 

Set  up  an  electric  bell  so  that  it  will  ring.  Trace  the  course  taken  by  the 
current  when  the  bell  is  set  ringing.  By  means  of  a  push  button  make  and 
break  the  circuit  and  note  results. 

Questions: 

.    I.  What  makes  the  clapper  move?    Why  does  it  fly  back  and  forth? 


336 


THE  WORK  OF  THE  WORLD 


2.  What  is  the  fundamental  principle  upon  which  the  operation  of  the 
electric  bell  depends? 

3.  Why  may  a  " run-down"  battery  stop  the  doorbell's  ringing? 

Diagram: 

Make  a  careful  diagram  of  an  electric  bell  in  your  notebook.  Label  all 
its  parts. 

PROBLEM  8:  How  DOES  A  TELEGRAPH  INSTRUMENT  WORK? 

Directions: 

Set  up  a  telegraph  instrument  and  trace  the  course  taken  by  the  current. 
By  means  of  the  sending  instrument  make  and  break  the  current  and  note 
the  result. 

Send  a  message  in  the  Morse  code. 


MORSE  TELEGRAPH  CODE 


Letters 

A 
B 
C 
D 
E 
F 
G 
H 
I 

K 
L 
M 
N 
O 
P 

Q 

R 

S 

T 

U 

V 

W 

X 

Y 

Z 


Morse 


Numerals 

Figures 

Morse 

I 



. 

2 



• 

3 



- 

4 

5 

—  

7 
8 

,. 

• 

9 

'.- 

0 



Punctuations 

.  Period 

:  Colon 

;  Semicolon  

,  Comma  • 

?  Interrogation 

!  Exclamation 

-  Fraction  Line 
If  Paragraph 
()  Parenthesis  


Questions: 

1.  What  makes  the  clicker  move? 

2.  What  is  the  fundamental  principle  upon  which  the  operation  of  the 
^telegraph  instrument  depends? 


COMMUNICATION  337 

PROBLEM  9:  How  DOES  A  TELEPHONE  WORK? 

Directions: 

What  are  the  names  and  uses  of  the  parts  of  the  transmitter  and  the 
receiver  that  can  be  seen  from  the  exterior? 

By  consulting  the  diagrams  on  page  345,  trace  the  course  taken  by  the 
current  in  both  parts  of  the  instrument. 

Of  what  use  are  the  particles  of  ground  carbon  in  the  transmitter? 
Summary: 

Name  two  fundamental  principles  or  laws  upon  which  the  use  of  the 
telephone  depends.  Explain. 

PROBLEM  10:  A  TRIP  TO  A  TELEPHONE  EXCHANGE. 

Directions: 

Try  to  obtain  answers  to  the  following  questions: 

How  does  the  operator  know  when  there  is  a  call? 

What  does  the  operator  do  when  she  puts  you  in  communication  with 
some  one  over  the  telephone? 

How  large  a  locality  is  served  by  the  exchange  you  visited? 

What  is  the  work  of  the  different  operators? 

How  are  long  distance  connections  made? 

Summary: 

Listen  attentively  to  what  is  told  you  on  the  trip  and  write  a  report  of 
your  visit. 

PROBLEM  1 1 :  A  TRIP  TO  A  NEWSPAPER  OFFICE. 

Directions: 

The  following  are  some  of  the  questions  that  should  be  in  your  mind 
while  making  the  trip: 

What  are  the  different  ways  in  which  news  is  collected? 

How  large  a  locality  is  served  by  the  newspaper? 

What  is  the  difference  between  local  and  foreign  news?  How  is  foreign 
news  obtained?  Has  the  paper  Associated  Press  service?  If  so,  what  is 
the  general  nature  of  the  news  thus  obtained? 

What  is  the  purpose  of  a  linotype  machine?  Of  a  monotype  machine? 
Observe  them  in  operation,  if  possible. 

How  many  papers  can  the  presses  print  in  one  hour?  If  possible,  observe 
them  in  operation. 

Summary: 

Listen  attentively  to  the  information  given  you  and  write  a  report  of 
your  visit  according  to  the  plan  suggested  in  the  questions. 

Organs  of  speech.  One  of  the  earliest  means  of  communication 
was  by  the  spoken  word.  No  one  knows  under  just  what  circum- 


338 


THE  WORK  OF  THE  WORLD 


stances  the  different  languages   have  come  into  existence,  al- 
though we  do  know  that  they  have  changed  and  are  changing. 

The  part  of  the  body  which 
makes  speaking  possible  is 
located  in  the  neck  in  the 
upper  part  of  the  wind-pipe 
or  trachea.  In  man,  it  is 
sometimes  called  the  Adam's 
apple,  although  it  is  more 
properly  termed  the  voice-box 
or  larynx.  It  consists  essen- 
tially of  two  cords  of  tissue 
that  can  be  moved  by  mus- 
cles. The  muscles  are  able 
to  hold  the  cords  in  such  a 
position  that  they  can  vi- 
brate when  air  is  forced 
through  them.  These  vibra- 
tions make  speaking  possi- 
ble. The  different  sounds 
that  the  human  voice  is  capa- 
ble of  making  are  also  partly 


FIG.  173.  Our  organs  of  speech,  i,  The  larynx; 
2,  view  from  above.  V,  Vocal  cords;  Mm, 
muscles  that  regulate  opening  and  closing  vocal 
cords,  and  L,  those  that  loosen;  T,  muscles  that 
tighten  the  vocal  cords. 


due    to    the    forms    of    the 
as  well  as  to  the  positions 


mouth,  throat  and  nasal  passages 

which  the  tongue  and  teeth  are  made  to  assume. 

Writing  and  printing.  Another  very  early  method  of  communi- 
cation was  by  writing.  At  first  the  forms  of  writing  were  very 
crude.  For  example,  pictures  and  symbols  were  chiseled  on 
stone.  Thus  the  early  Egyptians  wrote  what  we  now  call  hiero- 
glyphics. It  has  only  been  in  recent  years  that  some  of  these 
early  writings  have  been  deciphered.  Later,  a  system  of  letters 
was  evolved,  the  letters  standing  for  sounds,  certain  combina- 
tions of  which  would  form  words.  After  stones,  parchment  and 
paper  were  used  for  writing.  Then  it  became  necessary  to  use 
pencils  or  pens  and  writing  fluids. 

At  first  all  documents,  as  well  as  everything  else,  were  written 
Jby  hand.  It  was  not  until  the  fifteenth  century  that  a  printing 


COMMUNICATION 


339 


press  was  made.  To-day  some  of  the  great  printing  presses  are 
able  to  print  as  many  as  one  thousand  newspapers  a  minute.  In 
the  large  newspaper  offices  there  are  three  or  four  of  these  huge 
presses,  some  of  which  are  kept  busy  all  the  week  preparing  for 
the  remarkable  Sunday  editions.  Later  in  this  project  we  shall 
consider  other  facts  relating  to  the  making  of  newspapers. 

Signaling.  Probably  the  most  ancient  of  all  methods  of  com- 
munication was  by  signs  and  signals.  If  you  could  imagine  your- 
self shipwrecked  on  a 
coast  where  the  natives 
could  not  read,  write,  or 
speak  your  language,  you 
would  still  be  able  to  con- 
vey ideas  to  them  and  they 
to  you  by  means  of  mo- 
tions which  might  prop- 
erly be  called  a  sign  lan- 
guage. As  a  matter  of 
fact,  this  kind  of  language 
is  used  a  great  deal  even 
in  our  times  when  we  have 
wonderfully  developed 
methods  of  communicat- 
ing with  each  other. 

There  are  many  differ- 
ent methods  of  signaling. 
Boy  Scouts  learn  how  to 
signal  with  flags,  and  there 
is  a  very  important  branch 
of  the  military  service, 
known  as  the  Signal  Corps, 
where  the  men  are  taught 
many  methods  of  signal- 
ing, including  the  use  of 
the  wireless  telegraph. 

Electricity  and  modern 


FIG.  174.  A  member  of  the  Signal  Corps  using 
a  sunlight  flash  signaling  apparatus.  (Photograph, 
Committee  on  Public  Information.) 


methods  of  communication.      The 


electric  bell,  the  telephone,  the  telegraph,  submarine  cables,  and 


340  THE  WORK  OF  THE  WORLD 

the  wireless  telegraph  all  depend  upon  electricity  for  their  opera- 
tion. The  detailed  history  and  study  of  any  one  of  these  should 
take  the  form  of  an  individual  project.  We  cannot  here  do  much 
more  than  refer  to  the  most  fundamental  ideas  relating  to  these 
means  of  communication. 

When  you  have  worked  out  the  problems  suggested  at  the  be- 
ginning of  this  project,  you  will  see  what  a  fundamental  part  is 
taken  by  the  electro-magnet  in  modern  methods  of  communica- 
tion. If  you  understand  the  principle  of  the  electro-magnet,  it 
will  not  be  very  difficult  to  understand  the  arrangement  of  the 
different  devices  used  in  the  electric  bell,  the  telegraph,  and  the 
telephone.  You  will  understand  the  cause  of  the  ringing  of  the 
bell,  the  clickings  or  markings  on  a  tape  of  the  telegraph  instru- 
ment, and  the  vibrations  of  the  diaphragm  in  the  receiving  in- 
strument of  a  telephone.  In  order  to  understand  any  of  these 
things,  however,  it  is  first  essential  to  learn  about  magnetism. 

Magnets  and  lines  of  force.  The  property  possessed  by  mag- 
nets of  attracting  pieces  of  iron,  such  as  nails  or  tacks,  is  known 
by  every  one.  There  is  a  certain  ore  called  magnetite  because  it 
was  first  found  in  Magnesia,  Asia  Minor.  Another  name  for  it  is 
lodestone,  which  means  leading-stone.  It  was  given  this  name 
because  it  is  a  natural  magnet.  It  has  been  found  capable  of 
magnetizing  other  materials,  such  as  hard  iron,  by  rubbing  them 
in  one  direction  with  one  end  of  the  lodes  tone.  In  a  similar 
manner  a  steel  magnet  may  be  made  to  magnetize  a  piece  of  hard 
iron.  .  In  doing  this  neither  the  lodestone  nor  the  magnet  loses 
any  of  its  own  magnetism. 

The  reason  that  magnets  possess  the  property  of  attracting 
certain  other  objects  is  because  of  their  lines  of  force.  If  iron 
filings  are  sprinkled  on  a  paper  or  glass  directly  over  a  magnet, 
the  filings,  when  the  paper  or  glass  is  gently  tapped,  will  arrange 
themselves  in  a  certain  definite  manner.  It  will  be  noticed  that 
they  are  influenced  most  markedly  near  the  ends  or  poles  of  the 
magnet,  because  that  is  where  the  lines  of  magnetic  force  are 
strongest. 

Like  poles  repel;  unlike  poles  attract.  Each  little  iron  filing 
in  the  experiment  just  described  itself  becomes  a  magnet,  having 


COMMUNICATION  341 

a  north  or  positive  and  a  south  or  negative  pole.  It  assumes  a 
certain  definite  position,  because  it  is  affected  by  the  lines  of  force 
and,  being  small  and  light,*  is  able  to  move  easily.  Its  south  pole 
will  be  attracted  by  the  north  pole  of  the  magnet,  and  vice  versa. 

To  show  that  unlike  poles  attract  and  that  like  poles  do  not, 
it  is  only  necessary  to  place  the  different  ends  of  two  bar  magnets 
close  to  each  other  and  observe  the  results.  It  will  be  found  that 
when  two  north  poles  or  two  south  poles  are  placed  close  together 
there  is  no  attraction  between  them :  but  that  when  a  north  pole 
of  one  magnet  is  put  near  a  south  pole  of  the  other  magnet  an 
attraction  is  evident.  When  we  use  iron  filings,  as  directed  in 
problem  4,  we  can  see  that  while  an  attraction  exists  between 
two  unlike  poles,  two  like  poles  actively  repel  each  other. 

Permanent  and  temporary  magnets.  By  rubbing  a  lodestone 
or  an  iron  magnet  along  a  piece  of  hard  iron  it  is  possible  to  make 
a  magnet.  Such  a  magnet  is  a  permanent  one.  It  is  so  called 
because  it  retains  its  magnetism  after  it  has  been  taken  from  the 
other  magnet.  Permanent  magnets  are  distinguished  from  tem- 
porary magnets,  which  may  be  made  of  soft  iron,  such  as  a  nail. 
No  amount  of  rubbing  a  magnet  along  a  soft  piece  of  iron  will 
produce  a  permanent  magnet.  The  soft  iron  will  be  a  magnet 
only  as  long  as  it  is  kept  in  the  magnetic  field  of  the  permanent 
magnet.  Thus,  if  a  magnet  has  a  nail,  a  tack,  and  some  iron 
filings  clinging  to  it  in  a  more  or  less  straight  line,  they  will  tend 
to  stick  together  just  as  long  as  the  nail  is  magnetized  by  being 
kept  in  contact  with  the  magnet.  Just  as  soon,  however,  as  the 
nail  is  taken  from  the  magnet  it  loses  its  own  magnetism  and 
the  objects  will  fall  off. 

The  compass  and  its  uses.  A  compass  is  a  small  permanent 
magnet,  more  or  less  needle-like  in  form,  so  arranged  that  it  can 
move  freely  about  in  a  horizontal  plane.  For  many  centuries  it 
has  been  used  by  navigators  as  a  guide.  It  is  supposed  to  have 
originated  in  China  and  to  have  been  introduced  into  Europe  by 
the  Italian,  Marco  Polo,  about  1260  A.D.  At  first  a  piece  of  lode- 
stone  was  used  as  a  compass  and  later  permanent  magnets  were 
made  of  hard  iron. 

The  action  of  the  compass  depends  upon  the  fact  that  the  earth 


342 


THE  WORK  OF  THE  WORLD 


acts  like  a  huge  magnet,  having  its  magnetic  poles  fixed  and  situ- 
ated near  the  geographical  poles.     Therefore,  the  needle  swings 

approximately  into  a 
north  and  south  posi- 
tion. Before  the  dis- 
covery of  the  magnet  it 
was  necessary  to  use  the 
sun  and  stars  for  the 
purpose  of  ascertaining 
directions.  It  can  read- 
ily be  seen  that  on 
cloudy  days  or  nights 
it  would  be  extremely 
difficult,  if  not  impossi- 
ble, by  such  means  to  be 


FIG.  175.  A  compass,  marked  to  show  the  "points." 
(Courtesy,  Taylor  Instrument  Companies.) 


sure  of  directions.  The 
compass,  on  the  other  hand,  can  be  used  in  all  kinds  of  weather. 

It  is  true  that  what  is  referred  to  as  the  north  pole  of  a  magnet 
or  compass  is  in  reality  its  south  pole  in  that  it  is  attracted  to  the 
north  pole  of  the  earth.  In  like  manner,  the  so-called  south  pole 
of  the  compass  is  really  its  north  pole.  However,  scientists  have 
decided  to  call  the  north-seeking  pole  of  the  compass  the  north 
pole  and  the  south-seeking  pole  the  south  pole. 

Lines  of  force  about  an  electric  wire.  You  will  remember  that 
electricity  is  often  spoken  of  as  flowing  along  a  wire.  (See  page 
236.)  Oersted  of  Copenhagen,  in  1819,  made  a  very  remarkable 
discovery  which  has  made  possible,  as  we  shall  see  later,  the  pro- 
duction of  electric  bells,  telegraphs,  telephones,  and  electric  mo- 
tors. At  first,  however,  the  great  significance  of  the  discovery 
was  not  realized.  One  day  as  Oersted  was  working  in  his  labora- 
tory he  happened  to  notice  that  when  a  compass  was  brought 
near  a  wire  through  which  an  electric  current  was  flowing,  the 
needle  moved.  He  experimented  further  and  discovered  that 
there  was  a  magnetic  field  of  force  about  a  wire  carrying  an  elec- 
tric current. 

Making  an  electro-magnet.  By  wrapping  an  insulated  wire 
about  a  piece  of  soft  iron  and  sending  through  it  an  electric  cur- 


COMMUNICATION 


343 


rent,  the  iron  will  become  magnetized  as  long  as  the  current  con- 
tinues to  flow,  but  will  lose  its  magnetism  just  the  instant  the 
current  is  broken.  In  other  words,  under  the  influence  of  an 
electric  current  the  iron  becomes  a  temporary  magnet.  A  piece 
of  soft  iron  magnetized  through  the  effect  of  an  electric  current 
is  called  an  electro-magnet. 

In  addition  to  this  it  has  been  found  that  the  coil  of  charged 
wire  itself  is  a  magnet,  having  at  one  end  of  its  axis  a  north  and 
at  the  other  end  a  south  pole.  These  poles  can  be  made  to  change 
places  by  simply  reversing  the  direction  of  flow  of  the  electric 
current. 

The  electric  bell.  The  electric  bell  depends  for  its  operation 
primarily  upon  the  use  of  an  electro-magnet  produced  as  de- 
scribed'above.  The  clapper  of 
the  bell,  as  can  be  seen  in  the 
diagram,  is  attached  to  a  piece 
of  soft  iron.  This  piece  is  at- 
tracted to  the  other  pieces  of 
soft  iron  which  are  used  as 
cores,  having  the  wire  wrapped 
around  them.  The  bell  is  so 
made  that  when  the  clapper  is 
drawn  down  to  the  temporary 
magnets  producing  a  stroke 
upon  the  gong,  the  circuit  is 
immediately  broken.  Then  the 

iron    cores   lose    their   magnet-         FIG.  176.  An  electric  bell.  Find  the  electro- 
j,i  n          .  n       magnet  and  the  armature.    Explain  how  the 

ism  and  the  small  spring  pulls    push  button  works 
back  the  armature,  as  the  third 

piece  of  iron  to  which  the  clapper  is  attached,  is  called.  As  soon 
as  the  spring  draws  this  back,  however,  the  circuit  is  again  made. 
The  result  is  that  the  electric  current  again  flows  through  the 
wires  which  magnetize  the  cores  and  thus  the  bell  is  made  to  ring 
again.  This  action  is  produced  very  rapidly,  causing  the  rapid 
vibration  of  the  clapper  and  the  ringing  of  the  bell. 

The  telegraph.  The  telegraph  depends  upon  the  same  funda- 
mental principle  as  the  electric  bell.  In  this  case,  however,  the 


344  THE  WORK  OF  THE  WORLD 

spring  is  not  made  strong  enough  to  pull  the  sounder  back  unless 
the  current  is  broken.  This  is  done  by  releasing  the  pressure 

upon  the  button.  By  varying 
the  intervals  between  the  clicks 
it  is  possible  to  transmit  mes- 
sages by  means  of  a  code.  A 
very  short  interval  would  repre- 
sent a  dot ;  a  slightly  longer  one 
a  dash.  In  like  manner,  it  is  pos- 
FIG.  177-  A  telegraph  instrument.  Find  sible  by  attaching  a  writing  de- 

the  electro-magnet,  the  sounder,  and  the         .  1 

button.  vice  to  make  dots  and  dashes 

upon  a  moving  tape.     This  is 

done  by  holding  the  button  down  longer  at  one  time  in  order 
to  make  dashes  than  at  other  times  when  dots  are  to  be  made. 
In  either  of  these  ways  messages  may  be  sent  great  distances 
practically  instantaneously.  The*  advantages  of  using  a  tape 
are  that  it  does  not  have  to  be  deciphered  the  instant  the  mes- 
sage arrives,  and  that  a  permanent  record  is  made. 

When  the  telegraph  was  first  being  talked  about,  people  could 
not  believe  that  communication  between  distant  places  was  pos- 
sible. It  was  only  after  a  great  deal  of  hesitation  that  Congress 
appropriated  $30,000  to  set  up  a  telegraph  line.  This  line  was 
set  up  between  Washington  and  Baltimore  in  1844  when  Samuel 
Morse  sent  the  message  over  the  wire,  "What  hath  God  wrought! " 

Submarine  cables.  Shortly  after  telegraphy  on  land  became  an  assured 
reality,  it  occurred  to  some  people  that  it  might  be  possible  to  establish 
telegraphic  communication  across  the  Atlantic  Ocean.  Cyrus  W.  Field, 
an  American,  became  very  much  interested  in  this  idea,  and  in  1854  at- 
tempted to  lay  a  cable  between  Canada  and  Newfoundland  but  was  un- 
successful. The  next  year,  however,  he  succeeded  in  this  project.  Two 
years  later,  in  1858,  after  two  unsuccessful  attempts  during  which  the 
cables  broke  in  mid-ocean,  he  finally  succeeded  in  laying  a  cable  across  the 
Atlantic  Ocean.  This,  however,  was  only  a  partial  success,  since  too  large 
a  current  was  used  with  the  result 'that  the  cable  was  destroyed  after  the 
interchange  of  only  a  few  messages.  Not  disheartened  by  these  many 
failures  Cyrus  Field  again  in  1865  made  still  another  attempt,  and  after 
losing  one  thousand  miles  of  cable,  was  rewarded  with  success.  By  the 
use  of  submarine  cables,  to-day  we  receive  news  about  great  events  hap- 
pening in  Europe  fully  as  soon  as  the  people  living  in  European  cities.  Not 


COMMUNICATION 


345 


only  is  this  true,  but  the  whole  world  has  been  closely  connected,  because 
many  other  cables  have  been  laid,  some  in  other  oceans  besides  the  At- 
lantic. 

The  telephone.  The  operation  of  the  telephone,  like  that  of 
the  electric  bell  and  the  telegraph,  is  also  largely  dependent  upon 
the  use  of  electro-magnets.  There  are  certain  additional  prin- 
ciples underlying  the  operation  of  a  telephone,  however,  that 


FIG.  178.    The  parts  of  a  telephone.    D,  the  diaphragm 

make  it  somewhat  more  difficult  to  understand.  These  princi- 
ples are  partly  concerned  with  vibrating  objects  and  sound  waves. 
(See  page  16.)  The  reason  we  can  hear  when  the  receiver  is 
placed  to  the  ear  and  some  one  is  talking  into  the  transmitter  at 
the  other  end  of  the  wire  is  because  the  diaphragm  in  the  receiving 
apparatus  is  set  vibrating  in  exact  unison  with  the  diaphragm  in 
the  sending  apparatus.  In  the  transmitter  these  vibrations  are 
caused  by  the  sound  waves  from  the  speaker's  voice  hitting  the 
diaphragm  which  is  thereupon  set  vibrating.  The  vibrations 


346 


THE  WORK  OF  THE  WORLD 


alternately  make  and  break  the  current,  with  the  result  that 
an  electro-magnet  at  the  other  end  of  the  wire  attracts  the  dia- 
phragm in  the  receiver 
whenever  the  circuit  is 
completed  and  thus  causes 
it  to  vibrate.  (See  dia- 
grams.) 

The  name  of  Alexander 
Bell  should  be  associated 
with  the  telephone,  al- 
though many  others  con- 
tributed to  the  perfection 
of  the  instrument.  In  fact, 
it  should  be  understood 
that  no  one  man  is  alone 
responsible  for  the  produc- 
tion of  any  of  these  great 
instruments  toj  which  we 
have  been  referring.  They 
are  the  fruits  of  the  labors 
of  many  workers,  extend- 
ing back  to  Oersted  in 
1819  and  even  further, 
for  Oersted's  discovery 
could  not  have  been  made, 
had  not  others  before  his 
time  discovered  even  more  fundamental  principles. 

The  wireless  telegraph  and  telephone.  It  would  be  out  of 
place  here  to  go  into  a  detailed  study  of  the  wireless  telegraph  and 
telephone.  It  would  be  an  excellent  subject  for  an  individual 
project.  It  may  be  remembered  that  at  the  time  the  United 
States  entered  the  World  War  all  private  wireless  stations  had  to 
be  dismantled.  This  was  because  any  one  might,  if  his  apparatus 
was  properly  attuned,  pick  up  signal  messages  that  the  govern- 
ment would  desire  to  keep  secret. 

The  wireless  telegraph  and  telephone  depend  upon  sending 
great  electrical  waves  of  different  magnitudes  into  space.  These 


FIG.  179.    A  telephone  switchboard. 
(Courtesy,  Kellogg  Switchboard  and  Supply  Co.) 


COMMUNICATION  347 

waves  can  be  detected  by  a  properly  equipped  receiving  apparatus 
several  hundred  and  even  thousands  of  miles  from  their  source, 
and  if  the  code  is  known,  they  can  be  deciphered. 

One  of  the  most  wonderful  of  all  inventions  is  the  wireless 
telephone,  by  means  of  which  it  is  possible  to  hear  the  spoken 
word  at  great  distances  without  the  help  of  any  intervening  wires. 
For  the  perfection  of  both  the  wireless  telegraph  and  telephone 
the  world  is  chiefly  indebted  to  the  labors  of  Marconi,  who  while 
only  a  boy  began  the  study  which  later  enabled  him  to  be  of  such 
great  service  to  the  world. 

The  making  of  a  newspaper.  Everybody  is  familiar  with  news- 
papers. Perhaps  you  have  never  thought  very  much  about  just 
how  a  newspaper  is  made.  First,  it  is  necessary  to  collect  the 
news.  This  may  be  accomplished  by  reporters  who  for  the  most 
part  collect  local  news,  and  by  other  men  who  through  the  use  of 
the  telephone,  the  telegraph,  the  cables,  and  wireless  telegraphy 
report  events  happening  at  a  distance.  After  this  news  is  re- 
ceived, and  arranged,  it  then  becomes  necessary  to  set  it  in  type. 
Setting  up  type  was  formerly  entirely  done  by  hand.  In  recent 
years  the  ingenuity  of  some  men  has  resulted  in  producing  very 
wonderful  machines,  such  as  the  linotype  and  monotype.  The 
operator  sits  in  front  of  a  key-board  and  uses  keys  much  like 
those  of  a  typewriter.  As  the  letters  and  other  symbols  are 
touched  on  the  key-board,  metal  parts  drop  into  place.  The 
machine  then  presses  these  parts  automatically  against  molten 
metal  and  an  imprint  is  thus  made.  This  mass  of  metal  cools 
and  forms  a  line  of  type;  hence  the  name.  The  next  step  is  to 
put  the  type  in  place  in  large  " forms,"  each  of  which  represents 
a  page  of  the  newspaper.  These  forms  are  put  in  place  in  the 
great  presses  which  are  then  set  running.  The  presses  print, 
fold,  and  count  the  papers,  and  the  largest  ones  turn  out  as 
many  as  one  thousand  copies  a  minute.  Of  course,  the  large 
publishing  companies  also  make  use  of  these  machines  in  print- 
ing magazines  and  books. 

In  America  a  great  degree  of  efficiency  has  been  attained  in 
quickly  presenting  the  news  to  the  public.  As  a  striking  example 
of  this  fact,  it  is  well  known  that  when  Queen  Victoria  died, 


348  THE  WORK  OF  THE  WORLD 

extras  were  upon  the  streets  of  New  York  city  within  a  half  hour 
after  receiving  the  news.  This  was  considerably  ahead  of  the 
London  newspapers. 

INDIVIDUAL  PROJECTS 

Working  projects  : 

1.  Let  two  Boy  Scouts  or  two  Girl  Scouts  demonstrate  methods  of  signaling. 

2.  Demonstrate  experiments  with  wireless  telegraph  apparatus. 

The  Book  of  Wireless,     A.  F.  Collins.     D.  Appleton  &  Co. 

The  Book  of  Wonders.     Presbrey  Syndicate. 

Boy's  Book  of  Inventions.     R.  S.  Baker.  _  Doubleday  &  McClure. 

Romance  of  Modern  Inventions.     A.  Williams.     J.  B.  Lippincott  Co. 

Wireless  Telegraphy  and  Telephony.     A.  P.  Morgan.     Munn  &  Co. 

3.  Wire  for  buzzers  and  electric  door-bells. 

The  Book  of  Electricity.     A.  F.  Collins.     D.  Appleton  &  Co. 
Harper's  Everyday  Electricity.     D.  C.  Shafer.     Harper  &  Bros. 

Reports: 

1.  Iron  and  steel. 

The  Story  of  Iron  and  Steel.     J.  R.  Smith.     D.  Appleton  &  Co. 

2.  Morse,  the  inventor  of  the  telegraph. 

Great  Inventions  and  Discoveries.     W.  D.  Piercy.     Charles  E.  Merrill 

Co. 
The  Story  of  Great  Inventions.     E.  E.  Burns.     Harper  &  Bros. 

3.  The  making  of  a  book. 

Wonders  of  Science.     E.  M.  Tappan.     Houghton  Mifflin  Co. 

4.  Alexander  Bell  and  the  telephone. 

Stories  of  Inventors.     R.  Doubleday.     Doubleday,  Page  &  Co. 
Story  of  Great  Inventions.     E.  E.  Burns.     Harper  &  Bros. 

5.  The  wireless  telephone. 

Wireless  Telegraphy  and  Telephony.     A.  P.  Morgan.     Munn  &  Co. 

6.  The  Trans-Atlantic  cable. 

The  Story  of  the  Trans- Atlantic  Cable.     C.  Bright.     D.  Appleton  &  Co. 
Triumphs  of  Science.     M.  A.  L.  Lane.     Ginn  &  Co. 

7.  The  history  of  printing. 

Makers  of  Many  Things.     E.  M.  Tappan.     Houghton  Mifflin  Co. 
The  Story  Book  of  Science.     J.  H.  Fabre.     Century  Co. 

8.  Life  of  Edison. 

The  Boy's  Life  of  Edison.     Meadowcraft.     Harper  &  Bros. 

9.  The  liriotype  and  the  monotype  machines. 

Send  for  descriptive  catalogues. 

Book  of  Wonders.     Presbrey  Syndicate. 

10.  How  an  army  hears. 

Scientific  American  Supplement,  August  5,  1916. 

11.  Telephones  and  Forest  Rangers. 

Scientific  American  Supplement,  July  i,  1916. 

12.  Wireless  for  motor  boats. 

Scientific  American  Supplement,  June  24,  1916. 


PROJECT  XVII 
TRANSPORTATION 

Importance  of  transportation  in  everyday  life.  Almost  every- 
body at  times  finds  it  necessary  to  travel.  It  may  be  a  long  jour- 
ney across  a  continent  or  an  ocean  or  it  may  be  just  a  short  trip 
to  another  part  of  town.  If  a  long  trip  is  to  be  undertaken,  it 
involves  some  planning  and  the  utilization  of  some  outside  power, 
such  as  steam  or  electricity,  to  make  the  trip.  In  many  cases 
even  where  the  trip  is  a  short  one  we  also  use  power  other  than 
that  which  our  own  bodies  can  furnish.  Thus  we  drive,  motor,  or 
" trolley"  short  distances,  or  if  we  live  in  large  cities  we  may  take 
the  elevated  or  subway  trains. 

Even  if  we  -travel  but  seldom,  our  well-being  and  comfort  are 
almost  wholly  dependent  upon  the  use  of  systems  of  transporta- 
tion. Consider  where  many  of  the  things  came  from  which  you 
made  use  of  this  morning  before  going  to  school.  First,  you  had 
to  dress.  Did  your  father  raise  the  flax,  the  cotton,  etc.,  out  of 
which  your  clothes  were  made?  Did  your  mother  make  them 
in  your  home,  spinning  the  cloth,  dyeing  it,  etc.?  Did  your 
father  keep  the  cows  from  which  the  leather  of  your  shoes  came? 
Did  all  the  different  kinds  of  foods  upon  the  breakfast  table  come 
from  materials  grown  and  manufactured  upon  the  home  grounds? 
You  see  practically  everything  we  use  before  it  can  reach  us 
must  be  carried  perhaps  many  hundreds  or  thousands  of  miles. 

The  facilities  for  transporting  ourselves  and  goods  from  place 
to  place  are  so  common  that  perhaps  we  have  never  thought 
very  much  about  them.  We  know  in  a  general  way  that  great 
progress  has  been  made  in  methods  of  transportation  during 
recent  years.  Most  of  us,  however,  have  probably  given  little 
attention  to  such  questions  as:  What  makes  the  automobile, 
the  trolley-car,  the  subway  train,  the  locomotive,  the  steamship, 
or  the  airplane  move?  How  did  man  ever  discover  how  to  make 
such  truly  wonderful  things?  What  are  the  fundamental  princi- 


350  THE  WORK  OF  THE  WORLD 

pies  upon  which  their  operation  depends?     Some  of  these  ques- 
tions we  shall  attempt  to  answer  in  this  project. 

PROBLEMS 

PROBLEM  i :  WHY  DO  SOME  OBJECTS  FLOAT  IN  WATER? 
Directions: 

Fill  a  cup  with  water  and  stand  it  in  a  saucer.  Be  sure  the  cup  is  full 
and  the  saucer  is  dry.  Float  as  large  a  block  of  wood  as  possible  in  the  cup. 
What  happens?  Wipe  the  block  dry  and  weigh  it.  Weigh  the  water 
in  the  saucer.  Compare  the  two  weights.  If  the  wood  had  been  forced 
under  the  water,  would  the  weight  of  the  water  displaced  have  been  greater 
or  less  than  the  wreight  of  the  wood? 

Perform  the  above  experiment  with  an  object  which  sinks  in  water. 
How  does  the  weight  of  this  object  compare  with  the  weight  of  the  water 
displaced  by  it? 

Conclusion: 

From  the  above  experiments  what  can  you  conclude  regarding  the  rea- 
son why  some  objects  float  and  others  sink? 

PROBLEM  2:  WHAT  is  THE  SPECIFIC  GRAVITY  OF  IRON? 

Directions: 

Weigh  a  piece  of  iron.  Weigh  the  water  which  it  is  able  to  displace. 
(For  directions,  see  problem  i.) 

(Definition  —  By  the  specific  gravity  of  a  substance  is  meant  the 

number  of  times  it  is  heavier  or  lighter  than  the  weight  of  an  equal 

volume  of  water.) 
Conclusion: 

What  do  you  conclude  the  specific  gravity  of  iron  is? 

PROBLEM  3 :  WHAT  is  THE  PRINCIPLE  OF  THE  STEAM  ENGINE? 
Directions: 

Partly  fill  a  test-tube  with  water.  Put  a  snugly  fitting  cork  in  the  open 
end  and  heat  the  water  in  the  tube.  Make  the  water  boil.  Point  the  tube 
away  from  you  and  observe  what  happens  while  the  water  is  boiling. 

Question: 

How  do  you  explain  the  result  of  the  experiment? 

PROBLEM  4:  How  DOES  A  STEAM  ENGINE  WORK? 
Directions: 

If  possible,  obtain  a  model  of  a  toy  steam  engine.  Set  it  going  and 
observe  the  working  of  the  parts.  From  a  study  of  the  model  and  with  the 
help  of  the  diagram  on  page  357  try  to  obtain  answers  to  the  following 
questions. 


TRANSPORTATION 


351 


Questions: 

1.  What  makes  the  piston  move? 

2.  What  is  the  use  of  each  of  the  valves?     In  what  order  do  they  open 
and  shut?     Make  a  series  of  diagrams  to  illustrate. 

3.  How  is  the  motion  carried  from  the  piston  to  the  place  where  the 
work  is  to  be  performed?          ^ 

4.  How  does  the  steam  reach  the  piston  box? 

PROBLEM  5 :  WHAT  is  THE  PRINCIPLE  OF  A  GAS  ENGINE? 

Directions: 

Use  a  coffee  pot  prepared  by  making  a  hole  near  the  bottom  large  enough 
to  admit  a  Bunsen  burner.     Make  another  small 
hole  halfway  up  the  side.    A  wire  is  fastened  to 
the  handle  as  shown  in  the  diagram  at  C. 

Hold  a  flame  at  the  small  opening,  B.  Admit  gas 
at  the  lower  opening,  A.  What  happens?  When? 

Repeat  the  experiment.  How  many  times  does 
the  cover,  which  represents  the  piston  of  an  en- 
gine, fly  back? 

'  Empty  the  coffee  pot  of  the  products  of  com- 
bustion.    Try  the  experiment  again. 

When  the  mixture  fails  to  explode,  what  is  the 


reason? 

Conclusions: 

1.  What  causes  the  explosion  in  a  gas  engine? 

2.  What  is  one  of  the  conditions  necessary  for 
the  explosion  to  repeat  itself? 


FIG.  1 80.  An  apparatus 
to  show  the  action  of  a  gas 
engine. 

(Courtesy,  G.  A .  Cowen.) 


PROBLEM  6:  To  STUDY  THE  PARTS  OF  AN  ELECTRIC  MOTOR  AND  SEE  HOW 
IT  WORKS. 

Directions- 
Take  apart  and  set  up  a  small  electric  motor. 
Identify  the  following  parts:  the  permanent  magnets,  the  armature, 

the  commutator,  the  brushes  and  binding  posts.     Trace  the  course  taken 

by  the  electric  current  and  explain  what  it  is  that  makes  the  motor  move. 

(See  diagram  on  page  366.) 
Connect  the  motor  with  an  electric  current  and  use  it  to  run  as  many 

devices  as  possible. 

PROBLEM  7:  WHAT  is  THE  FUNDAMENTAL  PRINCIPLE  OF  A  DYNAMO? 

Directions: 

Attach  a  coil  of  insulated  wire  to  the  binding  posts  of  a  galvanometer. 
(Note  —  A  galvanometer  is  an  instrument  for  detecting  the  possible 
presence  of  an  electric  current.) 


352  THE  WORK  OF  THE  WORLD 

Thrust  a  permanent  magnet  in  and  out  of  the  coil  and  notice  whether 
the  galvanometer  indicates  that  there  is  an  electric  current  flowing  through 
the  wire. 

Conclusion: 
What  can  you  conclude  from  this  experiment? 

PROBLEM  8 :  To  VISIT  AN  ELECTRIC  POWER  STATION. 
Directions: 

If  necessary,  question  the  person  in  charge  of  the  trip  so  that  you  may  be 
able  intelligently  to  answer  questions  of  the  kind  here  given : 

What  is  the  source  of  the  power  from  which  the  electricity  is  generated? 

What  kind  of  turbines  are  used  and  how  much  power  do  they  generate? 

Where  are  the  magnets  and  where  are  the  revolving  armatures? 

Where  does  the  electricity  go  after  it  has  been  generated?  What  are  the 
different  ways  in  which  it  is  used? 

Summary: 

Write  a  report  of  your  trip,  explaining  at  least  two  of  the  devices  which 
you  saw. 

Animal  power  compared  with  steam  and  electric  power.    One 

of  the  earliest  methods  of  land  travel  was  the  caravan.  There 
were  several  well-known  caravan  routes  between  Asia  and  Europe. 
This  method  of  travel  was  entirely  dependent  upon  the  use  of 
animals.  Some  of  the  caravans  consisted  of  as  many  as  five 
thousand  camels  with  their  packs  and  drivers.  It  was  customary 
to  travel  in  large  companies,  sometimes  several  miles  long,  be- 
cause of  the  danger  from  robber  bands.  In  this  manner  materials 
could  be  exchanged  between  India  and  China  on  the  one  hand 
and  Asia  Minor  and  Europe  on  the  other. 

Animal  power  is,  of  course,  greatly  inferior  to  steam  and  elec- 
tric power.  At  the  present  time  the  amount  of  steam  power  used 
every  day  is  much  greater  than  the  combined  power  of  all  the 
horses  and  men  in  the  world.  Following  the  use  of  steam,  elec- 
tricity has  come  into  general  use,  and  although  they  have  been  in 
use  only  a  short  time,  now  the  electric  motor  and  dynamo  are 
considered  almost  indispensable. 

Water  as  a  means  of  transportation.  For  many  thousands  of 
years  man  has  used  water  for  the  transportation  of  himself  and 
goods  from  place  to  place.  Just  when  or  under  what  conditions 


TRANSPORTATION  353 

the  idea  of  building  a  boat  came  into  his  mind  we  do  not  know. 
Doubtless  the  possibility  of  doing  so  must  have  suggested  itself 
to  him  upon  observing  such  things  as  straws,  pieces  of  wood  or 
the  trunks  of  fallen  trees  floating  upon  the  surface  of  the  water. 
At  first  he  built  very  crude  small  boats  hollowed  out  of  the  trunks 
of  trees.  Later  he  learned  how  to  build  larger  ships  and  propel 
them  by  oars  or  sails.  Some  of  these  vessels  were  quite  large, 
accommodating  scores  of  rowers  and  passengers.  Still  later  iron 
was  used  for  the  hulls  of  ships.  By  that  time  it  had  become  pos- 
sible to  propel  the  ships  by  steam.  At  the  present  day  there  are 
great  ocean  liners  which  are  like  immense  floating  hotels,  able  to 
carry  hundreds  of  people  and  thousands  of  tons  of  merchandise. 

Why  substances  float  or  sink.  It  is  commonly  said  that  ob- 
jects lighter  than  water  float  and  objects  heavier  than  water  sink. 
What  does  this  mean  and  how  is  it  explained?  What  is  really 
meant  is  that  objects  lighter  in  weight  than  an  equal  volume  of 
water  float,  and  that  objects  heavier  than  an  equal  volume  of 
water  sink.  If  a  three-inch  iron  cube  were  placed  in  a  vessel  full  of 
water,  a  certain  amount  of  water  would  be  spilled  over  the  sides. 
If  this  quantity  of  water  were  carefully  measured,  it  would  be 
found  to  be  equal  in  volume  to  that  of  the  cube.  It  has  been 
determined  that  no  matter  what  the  object  is,  if  immersed  in 
water,  it  will  take  the  place  of,  or  displace,  a  volume  of  water 
just  equal  to  its  own  volume. 

Any  object  that  rises  to  the  surface  of  a  liquid  does  so  for  the 
same  reason  that  a  balloon  rises  above  the  ground.  As  soon  as 
the  weight  of  the  balloon  becomes  less  than  the  weight  of  the  air 
which  it  displaces  it  tends  to  rise.  Likewise,  a  piece  of  wood 
which  weighs  less  than  an  equal  volume  of  water  will  be  buoyed 
up  to  the  surface  when  placed  in  that  liquid. 

We  have  already  observed  that  the  pressure  within  any  part 
of  a  liquid  increases  with  its  depth.  (See  page  82.)  The  pres- 
sure at  any  point  below  the  surface  is  also  equal  in  all  directions. 
Thus,  point  A  in  our  diagram  would  have  an  equal  pressure  ex- 
erted upon  it  in  every  direction.  Let  us  suppose  that  a  block  of 
some  material  is  placed  in  a  liquid  so  that  its  top  surface  is  on  a 
level  with  A .  Let  us  also  suppose  that  the  pressure  at  this  point 


354 


THE  WORK  OF  THE  WORLD 


FIG.  181.  A  diagram  to 
show  why  objects  float  in 
water. 


is  five  ounces  per  square  inch.  Then  the  downward  pressure  will 
be  five  ounces  per  square  inch.  The  point  B,  being  lower  than  A , 
has  a  greater  pressure.  Let  us  suppose  that 
the  lower  surface  of  the  block  comes  on  a 
level  with  this  point,  and  that  the  pressure 
there  is  eight  ounces  per  square  inch.  It  is 
evident  that,  not  considering  the  weight  of 
the  block,  there  is  more  pressure  upon  it 
in  an  upward  direction  than  in  a  down- 
ward direction.  If  the  weight  of  the  block 
is  such  as  to  make  the  downward  pressure 
at  B  less  than  eight  ounces  per  square  inch, 
it  is  evident  that  the  block  will  be  pushed 
upward.  If,  however,  the  block  weig-hs  so 
much  that  its  weight  combined  with  the 
downward  pressure  at  A  will  be  greater  than 
the  upward  pressure  at  B,  the  block  will 
sink.  If  the  block  weighs  just  enough  to 
make  the  combined  downward  pressures 
equal  to  the  upward  pressure,  the  block  will  stay  stationary, 
neither  rising  nor  sinking. 

Archimedes'  principle.  The  principles  to  which  we  have  been 
referring  and  which  are  applied  in  the  floating  of  iron  ships  may 
be  stated  as  follows:  A  body  immersed  in  a  liquid  is  buoyed  up  by 
a  force  equal  to  the  weight  of  the  liquid  displaced.  It  was  first  formu- 
lated by  Archimedes,  a  Greek,  who  lived  about  250  B.C. 

The  king  of  Syracuse,  where  Archimedes  lived,  had  ordered  a  crown  to 
be  made  of  pure  gold.  After  it  had  been  made  he  suspected  that  some  sil- 
ver had  been  mixed  with  the  gold,  but  no  one  knew  how  to  find  this  out. 
The  king  asked  Archimedes  to  solve  the  problem,  and  for  a  long  time  Archi- 
medes puzzled  over  it.  It  is  said  that  one  day  when  stepping  into  the 
bath,  he  noticed  that  the  water  ran  over  the  sides.  It  occurred  to  him  that, 
if  he  put  the  crown  and  then  a  mass  of  pure  gold  of  the  same  weight  into  a 
vessel  full  of  water,  they  ought  to  cause  equal  amounts  of  water  to  flow 
over  the  sides  of  the  vessel.  However,  upon  doing  this,  he  found  that  the 
crown  caused  the  greater  amount  of  overflow,  thus  showing  that  it  was  of 
greater  bulk.  In  this  way  he  was  able  to  prove  that  the  crown  was  not 
made  of  pure  gold. 


TRANSPORTATION  355 

Specific  gravity.  The  term  specific  gravity  is  such  a  common 
one  that  it  is  well  for  us  to  know  what  it  means.  It  depends 
upon  Archimedes'  principle.  Broadly  speaking,  specific  gravity 
is  the  number  of  times  a  solid  or  liquid  is  heavier  or  lighter  than  an 
equal  volume  of  water.  If  an  object  is  heavier  than  water  the  spe- 
cific gravity  is  greater  than  one ;  if  it  is  lighter  than  water  the 
specific  gravity  is  less  than  one.  Thus,  for  a  piece  of  wood  the 
specific  gravity  may  be  .65,  while  for  gold  it  is  19.  Since  it  has 
been  found  that  the  specific  gravity  of  pure  substances  is  always 
the  same,  it  is  helpful  in  determining  the  nature  of  unknown  sub- 
stances to  find  out  their  specific  gravity. 

The  floating  of  iron  ships.  Objects,  such  as  large  stones,  which 
can  hardly  be  lifted  on  shore,  may  quite  readily  be  lifted  under 
water.  We  also  know  that  some  objects  such  as  wood,  the  specific 
gravity  of  which  is  less  than  one,  are  raised  to  the  surface  and 
float.  Certain  other  objects  such  as  rocks  and  pieces  of  iron 
sink,  because  their  specific  gravity  is  greater  than  that  of  water. 
A  hollow  piece  of  iron  may  be  made  in  such  a  way  as  to  float. 
Thus,  it  has  been  possible  to  make  ships  out  of  steel  because  the 
total  volume  of  the  ship,  including  the  air  enclosed  within  it, 
weighs  less  than  an  equal  volume  of  water. 

Submarines.  The  story  of  the  development  of  the  submarine 
is  too  long  to  tell  here.  It  will  make  an  individual  project  of 
intense  interest.  The  use  of  the  submarine  has  come  about  as  a 
development  of  Archimedes'  principle.  The  upward  push  of  the 
water  is  exactly  equal  to  the  weight  of  the  water  displaced.  The 
boat  rises  in  the  water  when  the  upward  push  is  greater  than  the 
weight  of  the  boat.  The  boat  can  be  made  to  sink  when  its 
weight  is  just  a  little  less  than  the  weight  of  the  water  displaced. 
Submarines  usually  contain  tanks  into  which  water  can  be  ad- 
mitted, thus  regulating  the  weight  of  the  boat.  The  direction  of 
movement  in  the  water  is  controlled  by  means  of  horizontal  rud- 
ders which  cause  the  boat  to  glide  either  upward  or  downward 
through  the  water  while  the  propeller  drives  it  forward. 

The  deeper  the  submarine  dives,  the  greater  the  water  pressure 
which  its  sides  must  withstand.  For  every  thirty- two  feet  in 
depth  the  pressure  increases  fifteen  pounds  per  square  inch.  In 


356 


THE  WORK  OF  THE  WORLD 


order  for  a  submarine  to  be  able  to  take  refuge  a  considerable  dis- 
tance below  the  surface  of  the  water,  as  was  sometimes  necessary 

r_ t  in  the  World  War,  its  sides  must 

be  built  strong  enough  to  resist  an 
immense  pressure. 

Steam  engines.  The  develop- 
ment of  steamships  has  depended 
upon  the  invention  and  develop- 
ment of  the  steam  engine.  The 
fundamental  principle  underlying 
the  operation  of  the  steam  engine 
is  that  when  water  is  changed  into 
steam  it  expands  with  great  force, 
occupying  approximately  sixteen 
hundred  times  the  amount  of  space 
it  formerly  occupied  as  water. 
This  expansive  force  is  used  to 
move  a  piston  which  is  connected 
by  shafts  to  the  wheels  of  the 
engine. 

The  first  steam  engine.  The 
steam  engine  originated  because 
of  the  necessity  of  getting  water 
out  of  coal  mines.  Some  mines 
had  to  be  abandoned  because  there 
was  no  way  of  removing  the  water. 
A  time  came  when  it  was  found 
absolutely  necessary  to  invent  a 
machine  that  could  •  accomplish  this  work.  There  is  probably 
no  better  illustration  of  the  old  saying  "Necessity  is  the  mother 
of  invention  "  than  the  invention  of  the  steam  engine.  After 
it  had  once  been  put  to  use  in  mines  it  soon  became  evident  that 
it  might  be  applied  in  other  ways  as  well. 

A  man  named  Newcomen,  in  1705,  invented  the  first  steam 
engine.  This  first  engine  really  depended  as  much  upon  air  pres- 
sure as  upon  steam  for  its  operation.  The  steam  was  admitted 
through  a  valve  into  a  piston  box  or  cylinder  and  forced  the  pis- 


FIG.  182.  A  submarine  coming  to  the 
surface. 

(Courtesy,  Scientific  American.) 


TRANSPORTATION 


357 


ton  to  move.  When  the  piston  had  traveled  the  entire  length  of 
the  cylinder,  a  spray  of  cold  water  was  introduced  into  the  interior 
of  the  cylinder  through  another  valve.  This  caused  a  condensa- 
tion of  the  steam  which  resulted  in  producing  a  partial  vacuum 
in  the  cylinder.  The  air  pressure  then  forced  the  piston  back  to 
the  starting  point.  The  valves  had  to  be  opened  and  closed  by 
hand  and  this  consumed  a  considerable  amount  of  time,  so  that 
the  number  of  strokes  that  this  engine  could  make  in  a  minute 
was  not  more  than  seven  or  eight.  There  is  a  story  in  connection 
with  this  first  steam  engine  to  the  effect  that  a  boy,  named  Hum- 
phrey Potter,  invented  a  system  of  levers  and  strings  which  me- 
chanically opened  and  closed  the  valves.  This  invention  made  it 
possible  for  the  engine  to  do  nearly  twice  as  much  work  as  previ- 
ously. 

How  a  steam  engine  works.     For  three  quarters  of  a  century 
Newcomen's  engine  was  the  only  one  known.     Then  in    1774, 


FIG.  183.  A  diagram  to  show  the  action  of  a  steam  engine.    The  movement  of 
the  piston  back  and  forth  in  the  cylinder  causes  the  flywheel  to  revolve. 

James  Watt  perfected  the  steam  engine,  improving  it  to  such  an 
extent  that  to  this  day  no  radical  changes  have  been  made  in  the 
way  steam  engines  are  made.  Watt's  engine  is  usually  spoken 
of  as  the  first  steam  engine,  although  Newcomen's  work  prepared 
the  way  for  it. 


358 


THE  WORK  OF  THE  WORLD 


The  fundamental  conditions 
necessary  for  the  operation  of 
the  double  acting  steam  engine, 
which  Watt  invented  in  1784, 
can  be  understood  by  referring 
to  the  diagram.  The  steam  en- 
ters the  steam  chest,  C,  through 
the  inlet,  i,  leading  from  the 
boiler,  which  is  not  shown  in 
the  diagram,  but  under  which 
there  is  a  fire  to  change  the 
water  into  steam.  After  enter- 
ing the  steam  chest,  the  steam 
is  carried  alternately  through 
two  passages  into  the  cylinder. 
This  alternate  use  of  the  two 
passages  is  brought  about  by 
the  sliding  valve,  which  is 
connected  with  the  revolving 
shaft  by  a  rod  called  the  ec- 
centric rod.  As  the  steam  en- 
ters one  end  of  the  cylinder  it 
moves  the  piston  toward  the 
other  end.  At  the  same  time 
the  steam  in  the  other  end  of  the 
cylinder  is  forced  out  through 
the  exhaust  pipe,  e. 

The  locomotive  and  the 
steamship.  Although  at  first 
nothing  but  stationary  steam 
engines  were  used,  it  was  not 
many  years  before  there  was  an 
attempt  to  make  vehicles  that 
could  be  propelled  by  steam. 
The  first  invention  of  this  kind, 
Cugnot's  steam  carriage,  in 
1769,  was  based  upon  Newco- 


TRANSPORTATION 


359 


men's  engine.  It  was  a  ponderous  mechanism  set  on  three  wheels 
with  a  fire-box  and  boiler  in  the  front.  The  making  of  steam 
carriages  that  would  travel  along  country  roads  was  not  success- 
fully accomplished  until  the  latter  part  of  the  nineteenth  century, 
when  some  of  the  auto- 
mobiles were  of  this  de- 
scription. In  the  early 
part  of  this  century,  how- 
ever, after  many  experi- 
ments on  the  part  of  sev- 
eral men,  Stephenson,  an 
Englishman,  constructed 
a  locomotive  which  he 
called  the  Rocket.  This 
locomotive,  in  1829, 
made  a  trip  from  Liver- 
pool to  Manchester.  The 
Rocket  was  able  to  at- 
tain a  speed  of  nearly 
thirty  miles  an  hour  and 
did  not  differ  markedly 
in  its  fundamental  fea- 
tures from  the  steam  lo- 
comotives of  the  present 
day.  Several  of  Stephen- 
son's  locomotives  were 
shipped  to  the  United 
States. 

Before  steam  was  successfully  used  for  propulsion  on  land, 
steam  power  was  applied  to  move  ships.  The  first  successful 
steamship,  called  the  Clermont,  was  constructed  by  Fulton  in  1807 
and  made  the  trip  from  New  York  to  Albany  and  back,  attaining 
a  speed  of  about  five  miles  an  hour.  To-day  there  are  magnificent 
steamships  plying  on  practically  all  the  great  rivers  and  lakes  of 
the  world  and  on  the  great  expanse  of  oceans.  As  an  example  of 
the  amount  of  transportation  that  depends  on  steamships,  con- 
sider the  fact  that  during  the  year  1918  more  than  two  million 


FIG.  185.  Hoisting  great  steam  turbines  aboard  a  liner. 
(Courtesy,  Cunard  S.S.  Co.  Ltd.) 


360 


THE  WORK  OF  THE  WORLD 


United  States  soldiers  were  transported  to  Europe  together  with 
more  than  enough  food  and  other  supplies  to  care  for  these  men. 
This  was  accomplished  in  spite  of  the  fact  that  attack  by  sub- 
marines had  to  be  guarded  against,  which  necessitated  the  pres- 
ence of  convoys  on  the  trips. 


FIG.  1 86.  Principal  steamship  routes  of  the  world. 

Great  water  routes.  The  ocean  is  the  world  highway.  A  nation  that 
does  not  touch  the  ocean  is  like  a  man  whose  house  is  not  on  a  street.  One 
cause  of  the  World  War  was  Germany's  desire  to  possess  more  easy  access 
to  the  ocean. 

Ships  that  sail  the  sea  may  be  divided  into  two  great  classes,  the  liners 
and  the  tramps.  Liners  carry  passengers,  mail,  and  a  certain  class  of 
goods,  such  as  small  expensive  articles.  Tramp  ships  do  a  much  greater 
proportion  of  the  work  of  the  world  than  most  people  realize.  They  carry 
the  heavy  commodities,  —  the  raw  materials  and  the  food,  which  are  neces- 
sary for  the  life  of  a  manufacturing  people.  The  two  kinds  of  ships  work 
together  as  freight  trains  and  express  trains  do. 

The  routes  of  the  liner  are  set,  within  certain  limits.  Each  has  a  sched- 
ule to  follow.  It  sails  from  an  American  port  and  docks  at  a  foreign  port, 
as  regularly  as  a  train  makes  a  trip,  except  as  occasionally  an  iceberg,  or  a 
storm  may  cause  the  usual  route  to  be  changed.  Tramps,  on  the  other 
hand,  go  wherever  a  cargo  awaits  them.  Sailing  ships  depend  on  the  great 
winds  of  the  world,  such  as  the  trade  winds  and  the  westerlies  for  favoring 
breezes.  Steamships  depend  more  upon  the  location  of  coaling  stations. 
Study  the  diagram  to  see  the  principal  steamship  routes. 


TRANSPORTATION  361 

Inland  commerce  depends  on  lakes  and  rivers.  In  the  United  States 
the  greatest  inland  waterway  is  the  Great  Lakes.  Since  water  transporta- 
tion is  always  cheaper  than  land  transportation,  most  of  the  railroads  ex- 
tending east  and  west  use  the  lakes  for  cheaper  transportation  of  their 
freight.  The  trade  routes  of  the  Middle  West  may  "  be  likened  to  a  section 
of  a  thick  cable  woven  of  many  strands  which  are  untwisted  and  spread  out 
fan-like  at  both  ends.  The  lakes  with  their  steamship  lines  and  the  com- 
peting railways  that  follow  their  shores,  make  the  central  or  compact  sec- 
tion of  the  cable.  The  loose  ends  are  represented  by  the  many  lines  of 
railway  that  converge  at  the  western  lake  ports,  and  by  the  other  lines 
that  diverge  from  the  eastern  lake  ports  to  the  Atlantic  Coast."  (J.  Russell 
Smith.)1 

Great  land  routes.  On  a  map  showing  the  railroads  in  the  United 
States  see  how  numerous  they  are  east  of  a  line  which  roughly  follows 
the  looth  meridian,  and  how  few  they  are  in  comparison  west  of  that 
line.  East  of  the  line  are  the  prairie  plains,  the  great  wheat-  and  corn- 
growing  district,  and  the  great  manufacturing  districts  of  the  country. 
The  flat  plains  offer  no  hindrance  to  railway  construction.  The  Appala- 
chian Mountains  are  not  too  high  to  cross  easily,  and  have  several  gaps 
through  which  railroads  may  pass.  The  Great  Lakes  offer  ports  with 
which  the  railroads  may  profitably  connect. 

West  of  the  looth  meridian  much  of  the  land  is  semi-arid.  The  ranges 
of  mountains  are  high  and  hard  to  cross.  The  population  is  scanty  com- 
pared with  that  of  the  East.  Trans-continental  trade  is  increasing  fast, 
however,  so  that  there  are  now  eight  distinct  ways  of  crossing  the  continent. 

Steam  engines  compared  with  gas  engines.  A  gas  engine  is  like 
a  steam  engine  in  that  both  use  fuel;  the  former  generally  uses 
gasoline,  while  the  latter  usually  burns  coal.  A  gas  engine  is  also 
like  a  steam  engine  in  that  both  need  an  air-supply.  They  are 
further  alike  in  that  they  produce  wastes  which  must  be  gotten 
rid  of.  Gas  engines  are  different  from  steam  engines  not  only 
because  they  are  lighter  and  consume  a 'different  kind  of  fuel,  but 
because  of  the  fact  that  these  engines  oxidize  the  fuel  in  the  cylin- 
der where  the  piston  operates ;  whereas  in  steam  engines  the  fuel 
is  consumed  in  the  fire-box  and  only  the  steam  enters  the  cylinder. 
For  this  reason  gas  engines  are  called  internal  combustion  engines. 

How  a  gas  engine  works.  In  a  gas  engine  there  are  four  strokes. 
(See  diagram.)  (i)  There  is  the  intake  stroke  during  which  the 
gas  and  air  are  mixed  and  sucked  into  the  cylinder  in  proper 

1  From  Industrial  and  Commercial  Geography,  Henry  Holt  &  Co. 


362 


THE  WORK  OF  THE  WORLD 


amounts.  (2)  There  is  the  compression  stroke  which  results  in 
compressing  the  mixture  of  gases.  (3)  There  is  the  power  stroke 
that  is  caused  by  the  explosion  of  the  gaseous  mixture  by  means 
of  an  electric  spark.  (4)  There  is  the  exhaust  stroke  which  cleans 
out  the  products  of  combustion  from  the  cylinder  and  thus  pre- 
pares it  for  another  series 
of  strokes.  Such  an  en- 
gine is  called  a  four  cycle 
engine. 

Although  most  gas  en- 
gines use  gasoline  there  are 
some  which  oxidize  other 
fluids.  Of  these,  the  Diesel 
engine  is  the  best  known. 
This  engine  is  now  used 
to  propel  some  ships,  for 
example,  the  submarine, 
and  is  more  economical 
than  the  gasoline  engine 
in  that  it  uses  a  cheaper 
form  of  fuel,  namely,  crude 
oil.  It  has  also  an  advan- 
tage over  the  gasoline  en- 
gine in  that  no  electric 
spark  is  needed,  the  heat 
of  the  compressed  gas  be- 
ing sufficient  to  cause  an 
explosion  of  the  mixture  at 
the  proper  time.  In  the 
gasoline  engine  the  cylin- 


tiG.  187.  A  gas  engine.  The  four  cylinders  show 
the  pistons  in  the  positions  at  the  beginning  of  the 
four  strokes.  A,  the  power  stroke,  when  the  ex- 
plosion forces  the  piston  to  descend;  B,  the  exhaust 
stroke  when  the  gases  pass  out  of  the  pipe  at  the 
top,  and  the  piston  ascends;  C,  the  compression 
stroke;  D,  the  intake  stroke. 

(Courtesy,  McQuay-N orris  Manufacturing  Co.) 


ders  have  to  be  kept  cool  so  that  the  gaseous  mixture  does  not 
explode  prematurely.  This  is  just  the  opposite  of  the  steam  en- 
gine where  it  is  of  advantage  to  keep  the  cylinder  hot.  Can  you 
see  why? 

The  automobile.  As  early  as  the  eighteenth  century  Cugnot 
invented  a  steam  carriage,  but  for  many  reasons  such  forms  of  lo- 
comotion did  not  come  into  general  use  at  that  time.  It  was  not 


TRANSPORTATION 


363 


n  b* 


until  half  a  century  later  that  any  considerable  attention  was 
again  given  to  this  problem. 
Again  the  effort  was  doomed 
to  fail.  It  was  not  until  near 
the  end  of  the  nineteenth 
century  that  the  problems 
involved  in  producing  a  self- 
moving  vehicle  were  success- 
fully solved.  At  that  time 
three  kinds  of  automobiles 
were  manufactured:  one  ob- 
taining its  power  from  steam ; 
another  from  electricity ;  and 
the  third  from  gasoline. 

In  the  usual  type  of  gaso- 
line motor  car,  the  gasoline  is 
drawn  from  the  gasoline  tank 
(A)  into  the  carburetor,  not 
shown  in  the  diagram,  where 
it  is  changed  from  a  liquid 
into  a  gas  by  being  forced 
through  very  small  openings. 
In-rushing  air  carries  the  gas- 
oline vapor  into  the  motor 
cylinders  (B).  A  proper  ad- 
justment of  the  carburetor  is 
necessary  in  order  that  the 
gas  and  air  s.hall  be  mixed  in 
just  the  right  proportions  to 
produce  an  explosion  (see 
problem  5). 

In  each  motor  cylinder  the 
same  cycle  of  changes  takes 
place : 

(i)  In  the  intake  stroke  the 
valves  at  the  top  of  the  cylinder  are  open  to  allow  the  mixed  gas 
and  air  to  enter  as  the  piston  (C)  descends. 


364 


THE  WORK  OF  THE  WORLD 


(2)  In  the  compression  stroke  the  intake  valves  are  closed  as  the 
piston  moves  upward,  compressing  the  mixture. 

(3)  In  the  power  stroke  a  spark  from 
the  spark  plug  causes  the  explosion  of 
the  mixture  of  gas  and  air.    The  pres- 
sure  of    the   expanding  gases  forces 
the  piston  to  descend.   The  connect- 
ing rod   (D)    is   connected  with   the 
crank  shaft  (£),  which  turns  the  fly- 
wheel (F).  | 

(4)  In  the  exhaust  stroke  the  piston 
moves  upward,  forcing  the  burned  gas 
through  an  exhaust  valve  into  the  ex- 
haust pipe. 

After  the  engine  is  started,  either 
by  a  crank  or  by  an  electric  starting 
system,  this  series  of  strokes,  taking 
place  at  slightly  different  times  in  the 
cylinders,  keeps  the  flywheel  in  mo- 
tion and  transmits  its  power  by  means 
of  the  propeller  shaft  (G)  and  tfie 
transmission  (H)  to  the  rear  axle  (7),  which  turns  the  wheels. 
The  transmission  is  a  change-speed  device  consisting  of  gears 
which  mesh  with  each  other  in  dif- 
ferent combinations  controlled  by  the 
change-speed  lever  (/).  In  "low" 
gear  the  speed  of  the  car  is  slowest. 
When  the  gears  are  shifted  to  "inter- 
mediate" or  "second,"  the  speed  is 
somewhat  increased.  "High"  or  "di- 
rect" speed  is  used  in  running  the  car 
after  it  is  started. 

The  car  is  kept  in  motion  by  the 
rear  axle  drive  (K).  By  a  system  of 
gears  the  motion  of  the  propeller 

shaft  causes  the  axle  shaft  to  turn  the  wheels.  The  type  of  gear 
shown  in  the  truck  illustrated  is  known  as  a  worm  drive.  It 
operates  on  the  principle  of  a  screw  (see  page  329). 


FIG.  189.  A  gear-shift  in  an 
"automobile. 

(Courtesy,  New  Departure  Mfg.  Co.) 


FIG.  190.  The  worm  drive. 
(Courtesy,  New  Departure  MJg.  Co.) 


TRANSPORTATION 


365 


In  1895  the  first  automobile  race  in  this  country  was  held  at  Chicago. 
The  course  was  ninety-five  miles  long.  Two  machines  entered  and  one 
did  not  finish.  The  one  that  finished  maintained  an  average  speed  of  ten 
miles  an  hour  and  was  forced  to  make  several  stops  for  repairs  and  for  the 
purpose  of  packing  ice  around  the  engine. 

Compare  this  condition  of  affairs,  only  a  little  over  twenty  years  ago, 
with  the  automobile  of  to-day!  The  automobile  is  said  to  have  made  it 
possible  for  the  French  to  stop  the  Germans  at  the  Marne  in  1914,  when  in 
one  night  sixty  thousand  troops  were  taken  out  forty  miles  from  Paris  in 
automobiles.  Consider  the  many  diversified  uses  to  which  the  automobile 


Revolving  Turret—^ 
Machine-Gun  or  Cannon  \ 


Speed  AW!  Steering 
Entrance  Door*  rs" 


xExit  Door 
/  .Gasolene  Tank 

'     "'  Ventilator 


/Radiator 
,  Engine 

Tail  for  Trench- 
Climbing 


te^^^^fsc^^r  j 


Disconnecting     slj)river.  ;         *  Crank  for  Starting 
Lever  and  Brake  •  Gunner 


Apparatus  for  Irani-* 
nutting  Power  from 
Engine  to  Whe<?ia 


FIG.  191.  A  French  tank.  A  light  tank,  weighing  about  seven  tons,  is  pictured.  It 
can  cut  through  barbed  wire  as  if  it  were  straw,  and  crash  through  masonry  walls.  It 
has  a  low  center  of  gravity,  which  prevents  its  capsizing.  Its  movement  depends 
upon  a  chain  tread  which  plays  upon  wheels  which  are  connected  with  the  motor. 

.  (Courtesy,  American  Review  of  Renews.) 


is  put  during  war-times.  How  many  lives  have  been  saved  by  this  fast- 
moving  vehicle  in  transporting  the  wounded  quickly  to  dressing-stations 
and  hospitals!  From  the  other  viewpoint,  what  terrible  machines  of  de- 
struction, such  as  ''tanks,"  has  the  automobile  made  possible! 

Electric  power.  In  most  large  towns  and  in  every  city  through- 
out the  United  States  there  are  numerous  examples  of  our  de- 
pendence upon  electricity  for  transportation.  Thus,  the  motion 
of  trolley  cars,  cable  cars,  elevated  and  subway  trains  depends 
upon  electricity.  All  of  these  conveniences  depend  upon  electric 
motors  for  their  operation  and  electric  motors  depend  upon  the 


366 


THE  WORK  OF  THE  WORLD 


electro-magnet.  We  have  already  studied  about  electro-magnets 
in  connection  with  electric  bells,  telegraphs  and  telephones,  and 
we  shall  need  to  review  this  subject  here.  (See  pages  342- 

347-) 

The  parts  and  working  of  an  electric  motor.   By  the  use  of  elec- 
tro-magnets so  placed  as  to  be  able  to  revolve  in  the  field  of 

force  of  permanent  magnets,  it  is  pos- 
sible to  change  electrical  energy  into 
the  energy  of  motion.  This  can  be 
understood  by  referring  to  such  a 
simple  diagram  as  the  one  at  the  side 
of  the  page.  A  permanent  magnet  is 
arranged  as  indicated  with  unlike  poles 
at  one  end.  The  temporary  magnets 
with  coils  of  wire  wrapped  around 
them  are  free  to  move  upon  an  axis, 
which  is  situated  between  the  un- 
like poles  of  the  permanent  magnet. 
These  coils  of  wire  are  connected  in 
such  a  way  with  other  wires  carrying 
electric  currents  that  as  soon  as  these 
magnets  revolve  from  position  3  to 
position  4,  the  current  is  automati- 
cally reversed  in  each  of  the  coils.  Therefore  what  was  formerly 
a  south  pole  becomes  a  north  pole  and  vice  versa.  This  results  in 
there  being  a  constant  attraction  and  repulsion,  as  shown  in  the 
diagram,  and  the  electro-magnets  with  their  coils  are  made  to  re- 
volve very  rapidly.  The  manner  of  connecting  the  coils  with 
the  electric  current  is  not  shown  in  the  diagram.  This  can  best 
be  studied  in  the  laboratory  by  examining  a  small  motor. 

Electric  cars  and  locomotives.  Although  the  motion  of  all 
electric  cars  is  dependent  upon  the  use  of  electric  motors,  there  are 
several  different  ways  in  which  the  electricity  is  brought  into  the 
motor  from  the  power-station  or  plant.  Thus,  in  the  case  of  a 
trolley  car  the  electric  current  is  conducted  in  overhead  wires  and 
led  by  means  of  a  pole  down  to  the  motors  which  are  placed  under 
the  cars.  There  are  usually  eight  motors  to  a  car.  JThe  electric 


FIG.  192.  A  diagram  to  show  the 
principle  of  an  electric  motor. 


TRANSPORTATION 


367 


circuit  is  completed  through  the  ground  and  through  the  tracks. 
In  the  case  of  a  cable  car,  the  wire  carrying  electricity  is  placed 
underground  and  the  pole  connects  with  it  underground  instead 
of  overhead.   There  is  still 
another  common  method 
of  conducting  the  electric- 
ity, namely,  by  means  of 
the    so-called     third    rail 
which  is  placed  alongside 
of  the  tracks.    This  third 
rail    carries    the    current 
which  is  in   turn  brought 
to  the  motors  under  the 
car  by  means  of  a  shoe  or 
iron  connection. 

Electric  locomotives 
have  recently  been  in- 
stalled for  limited  dis- 
tances over  roads  which 
formerly  carried  only 
trains  pulled  by  steam  lo- 
comotives. One  of  the 
great  advantages  of  the 
electric  locomotive  is  that 
it  produces  no  soot  and 
smoke.  Therefore  it  is 
especially  to  be  desired 
while  trains  are  passing 

through  cities.  The  New  York  Central  Railroad  uses  electric 
locomotives  57  feet  long  and  weighing  1 10  tons.  They  are  driven 
by  8  motors,  each  of  325  horse-power.  The  largest  electric  lo- 
comotives that  have  been  built  are  used  on  the  Chicago,  Mil- 
waukee &  St.  Paul  Railway.  These  weigh  260  tons,  are  112  feet 
long  and  are  capable  of  developing  3440  horse-power. 

The  dynamo  compared  with  the  electric  motor.  In  one  sense 
the  dynamo  is  the  opposite  of  the  electric  motor.  The  object  of 
the  motor  is  to  obtain  motion  and  in  doing  so  it  makes  use  of  elec- 


FIG.  193.  An  electric  locomotive. 
(Courtesy,  New  York  Central  Lines.) 


368 


THE  WORK  OF  THE  WORLD 


tricity.     The  object  of  the  dynamo  is  to  generate  electricity  and 
in  doing  so  it  uses  the  energy  of  motion.     (See  page  212.) 

The  principle  of  the  dynamo.  As  the  electric  motor  depends  for 
its  operation  upon  the  electro-magnet,  so  also  does  the  operation 
of  the  electric  dynamo.  Faraday,  an  English  scientist,  discov- 
ered in  1831  the  principle  upon  which  all  dynamos  are  run.  He 
found  that  when  a  permanent  magnet  is  placed  inside  of  a  coil  of 
wire  through  which  an  electric  current  is  flowing,  that  a  tem- 
porary current  is  produced  in  the  wire  and  that  another  current  is 
produced  when  the  magnet  is  withdrawn.  Here  was  a  means  of 

producing  or  generat- 
ing electricity,  provided 
there  was  a  supply  of 
motion  energy  available 
to  produce  a  movement 
of  the  coils  so  as  to  con- 
tinually cut  through  the 
lines  of  force  about  the 
magnet.  The  principle 
of  the  dynamo  is  easily 
understood,  if  the  elec- 
tric motor  has  been  stud- 
ied. The  best  way  to 
study  a  dynamo  is  to 
set  one  in  operation  and 
study  its  parts,  which 
will  be  found  to  be  quite 


FIG.  194.  Using  the  power  of  Niagara.  The  banks 
of  the  river  below  the  Falls  are  lined  with  factories 
where  a  part  of  the  tremendous  power  of  Niagara  is 
used.  Some  of  the  water  may  be  seen  returning  to 
the  river  after  turning  wheels  in  the  factories. 


similar  to  the  electric 
motor,  except  in  a  re- 
versed position,  the  elec- 
tricity coming  away  from 
or  out  of  the  machine 

rather  than  going  into  it.     The  dynamo  is  run  by  the  power  of 

falling  water  or  by  the  pressure  exerted  by  water  changing  into 

steam. 

Power  stations.     The  power  plants  in  the  United  States  for 

1917  have  been  estimated  as   constituting  a   contribution  of 


TRANSPORTATION 


369 


$555,000,000  to  the  national  wealth.  These  plants  make  it  pos- 
sible for  electric  railways,  manufacturing  of  many  kinds,  the  tele- 
graphs, the  telephones,  and  many  other  industries  to  be  conducted. 
Altogether  the  value  of  electrical  industries  for  1917  approximated 
considerably  over  $2,500,000,000. 

More  and  more  an  increasing  number  of  dynamos  are  being 
run  by  water-power  instead  of  by  steam.  Three  great  water- 
power  plants  may  be  mentioned.  The  two  largest  in  the  United 
States  are  situated  at  Niagara  Falls,  New 
York,  and  at  Keokuk,  Iowa.  Any  points 
within  a  radius  of  200  miles  of  these  places 
may  obtain  electric  power  from  these 
stations.  St.  Louis,  137  miles  away  from 
Keokuk,  consumes  most  of  the  power  gen- 
erated at  that  place.  The  falls  of  the 
Feather  River,  in  the  northern  part  of 
California,  furnish  power,  some  of  which 
is  used  in  San  Francisco,  160  miles  away. 
The  dynamos  in  large  power  plants  are 
run  by  great  water-wheels. 

Kinds  of  water-wheels.  There  are  three 
kinds  of  water-wheels:  the  over-shot,  the 
breast-wheel,  and  the  under-shot.  As  these 
names  imply,  the  over-shot  wheel  receives 
the  water  from  above;  the  breast-wheel 
receives  it  almost  at  the  middle;  and  the 
under-shot  wheel  receives  it  underneath. 
If  you  will  examine  the  illustrations,  you 
will  be  able  to  understand  the  operation 
of  these  wheels.  The  over-shot  wheel  re- 
ceives the  water  in  buckets,  the  weight  of 
which  forces  the  wheel  to  revolve.  The 
breast-wheel  works  in  a  similar  manner. 

The  under-shot  wheel  has  paddles  which  are  moved  by  swiftly 
flowing  streams  of  water.  It  is  this  latter  variety  which  is  used 
in  the  case  of  the  powerful  water  turbines,  which  are  made  in 
such  a  way  that  practically  all  of  the  force  of  the  water  is  used. 


FIG.  195.  Three  types  of 
water-wheels. 


370  THE  WORK  OF  THE  WORLD 

In  the  case  of  most  of  these  wheels  the  power  is  transferred 
to  the  machines  by  means  of  leather  belts,  as  you  may  see  in 
the  accompanying  diagrams.  Because  of  its  greater  power  the 
turbine  motor  is  now  in  more  general  use  than  the  other  kinds. 
All  large  water-power  plants  are  equipped  with  them.  It  is  pos- 
sible by  their  use  to  generate  electricity,  which  as  has  already 
been  noted,  may  be  carried  many  miles  to  the  places  where  its 
power  is  needed. 

Forests  regulate  the  flow  of  water.  There  is  a  close  connection 
between  the  safeguarding  of  water-power  and  the  protection  of 
forests.  This  relationship  is  due  chiefly  to  the  nature  of  the  soil 
in  forests.  The  soil  consists  largely  of  fallen,  decaying  leaves 
and  wood,  held  in  place  by  the  many  entangled  roots  of  trees.  It 
is  spongy  to  the  touch.  As  most  streams  start  far  up  on  the  heav- 
ily wooded  sides  of  mountains,  their  sources  and  the  banks  for 
many  miles  from  their  sources  are  lined  with  thick  growths  of 
trees.  These  forests  help  to  regulate  the  amount  of  water  that 
flows  in  the  stream.  They  prevent  flooding  in  the  spring  and 
drying  in  the  summer.  The  water  from  the  heavy  snows  of  win- 
ter and  the  heavy  rainfalls  of  spring  is  absorbed  by  the  spongy 
soil  of  the  forest.  It  can  pass  only  very  slowly  through  this  kind 
of  soil.  In  places  where  forests  have  been  destroyed,  the  forest 
soil  is  eventually  washed  away,  since  there  are  no  longer  any 
roots  to  hold  it  in  place,  and  when  this  is  done  there  is  no  way  of 
holding  the  water  back  so  as  to  avoid  floods  in  the  spring  and 
drought  in  the  summer.  How  do  you  explain  the  fact  that  cut- 
ting down  the  forest  may  result  in  a  blocked  harbor  hundreds  of 
miles  away? 

Methods  of  protecting  forests.  Forests  need  protection  most 
against  destruction  by  fire  and  by  wasteful  lumbering. 

Lookouts  or  forest-wardens  should  be  stationed  on  high  points 
overlooking  the  forests  for  the  purpose  of  warning  the  people  in 
the  nearest  settlement  of  any  suspicious  appearance  of  smoke  in 
the  forest.  Forest-fire  fighters  are  often  able  to  extinguish  a  fire 
in  the  early  stages  before  it  can  do  great  damage.  Campers 
should  be  very  careful  to  put  out  their  fires  before  leaving  them. 
It  should  be  realized  that  a  fire  sometimes  smoulders  quite  far 


TRANSPORTATION  371 

beneath  the  surface  when  it  apparently  has  been  entirely  extin- 
guished. It  is  better  to  build  a  camp-fire  on  rocks  rather  than  on 
the  spongy  soil,  but  if  the  fire  is  built  on  the  soft  soil,  it  is  well  to 
soak  the  water  thoroughly  all  around  before  leaving  it.  Locomo- 
tives passing  through  forest  regions  should  be  required  to  burn  oil 
instead  of  coal.  This  is  done  in  some  places,  such  as  the  Adiron- 
dack Mountains.  How  does  this  help  to  prevent  forest  fires? 

The  forests  are  one  of  our  greatest  national  resources  and  they 
should  be  protected  against  greed  and  ignorance.  In  the  past 
there  have  been  instances  on  record  where  selfish  individuals  and 
corporations,  after  having  received  permission  from  the  Govern- 
ment under  false  pretexts,  have  proceeded  to  cut  down  the  for- 
ests in  a  wholesale  manner.  Their  methods  have  resulted  in  the 
destruction  of  smaller  trees  as  well  as  of  the  larger  and  older  ones. 
Laws  and  strict  enforcement  of  them  are  needed  to  protect  the 
forests  by  requiring  certain  methods  of  lumbering.  National  and 
State  Governments  can  provide  for  forest  reservations  where  no 
lumbering  shall  be  permitted  except  for  public  use.  Steps  of  this 
kind  have  been  taken  in  many  places  through  the  United  States, 
but  more  activity  of  this  sort  is  desirable. 

INDIVIDUAL  PROJECTS 

Working  projects: 

1.  Explain  and,  if  possible,  demonstrate  the  working  of  certain  parts  of  an 
automobile. 

The  Automobile.     Zerbe. 

2.  Set  up  an  electric  motor  and  demonstrate  how  it  works. 

3.  Make  water-wheels  and  demonstrate  them. 

Harpers'  Machinery  Book  for  Boys.     J.  H.  Adams.     Harper  &  Bros. 
Practical  Things  with  Simple  Tools.     M.  Goldsmith.     Sully  &  Klein- 
teich. 

4.  Make  a  boat. 

The  Outdoor  Handy  Book.     D.  C.  Beard.     Chas.  Scribner's  Sons. 

5.  Make  electrical  toys. 

Home~Made  Toys  for  Girls  and  Boys.     A.  N.  Hall.     Norwood  Press. 

Reports: 

i.  Submarines. 

Boys'  Book  of  Inventions.     R.  S.  Baker.     Doubleday  &  McClure. 
The  Boys'  Book  of  Submarines.     V.  D.  Collins.     Fred  A.  Stokes  Co.   . 
The  Book  of  Wonders.     Presbrey  Syndicate. 
The  Romance  of  Modern  Mechanism.     A.  Williams.     J.  B.  Lippincott 

Co. 
Stories  of  Inventors.    R.  Doubleday.     Doubleday,  Page  &  Co. 


372  THE  WORK  OF  THE  WORLD 

The  Story  of  the  Submarine.     Bishop.     Century  Co. 

Submarines,  their  Mechanism  and  Operation.     F.  A.  Talbot.     J.  B. 

Lippincott  Co. 
Triumphs  of  Science.     M.  A.  L.  Lane.     Ginn  &  Co. 

2.  Gas  engines. 

The  Book  of  Wonders.     Presbrey  Syndicate. 
Chemistry  of  Common  Things.     Brownlee.    Allyn  &  Bacon. 
The  Romance  of  Modern  Mechanism.     A.  Williams.     J.  B.  Lippincott 
Co. 

3.  Ships  and  shipbuilding. 

How  It  Is  Done.     A.  Williams.     Thos.  Nelson  &  Sons. 
The  Origin  of  Inventions.     O.  T.  Mason.     Chas.  Scribner's  Sons. 
The  Romance  of  the  Ship.     E.  K.  Chatterton.     J.  B.  Lippincott  Co. 
Story  of  Useful  Inventions.     S.  E.  Freeman.     Century  Co. 

4.  Automobiles. 

The  Automobile.     Zerbe. 

Stories  of  Inventors.     R.  Doubleday.     Doubleday,  Page  &  Co. 

5.  Steam  engines  and  locomotives. 

Careers  of  Danger  and  Daring.     C.  Moffett.     Century  Co. 

Great  Inventions  and  Discoveries.     W.  D.  Piercy.     Chas.  E.  Merrill  Co. 

The  Locomotive.     Hartford  Steam  Boiler  Co. 

The  Romance  of  Modern  Locomotion.   A.  Williams.    J.  B.  Lippincott  Co. 


PROJECT  XVIII 
LIFE  —  ITS  ORIGIN  AND  BETTERMENT 

The  changing  life  upon  the  earth.  Have  you  ever  thought 
what  a  great  multitude  of  living  things  inhabit  our  world?  You 
can  hardly  go  anywhere  without  seeing  some  forms  of  life.  Most 
living  things  are  found  on  the  surface  of  the  ground  or  in  the 
waters  that  cover  such  a  large  part  of  the  earth.  There  are  also 
creatures  which  spend  a  large  part  of  their  lives  in  the  air  and 
others  that  live  underground.  Questions  concerning  the  origin, 
development,  and  length  of  time  these  living  things  have  existed 
upon  the  earth  have  perplexed  scientists  for  centuries.  Probably 
some  of  these  questions  will  never  be  definitely  answered. 

A  study  of  the  upper  layers  of  rock  which  help  to  form  the 
earth's  surface  has  shown  the  imprints  and  remains  of  plants  and 
animals  that  lived  in  past  ages.  By  means  of  such  a  study  scien- 
tists have  determined,  for  example,  that  the  horse  was  at  one 
time  an  animal  the  size  of  a  large  dog ;  that  ferns  grew  as  large  as 
trees;  and  that  dragon-flies  once  had  wings  several  feet  long.  It 
is  probable  that  all  plants  and  animals  with  which  you  are  most 
familiar  are  quite  different  now  from  what  their  ancestors  were 
at  one  time.  This  great  fact,  namely  that  during  the  many  hun- 
dreds of  thousands  of  years  that  life  has  existed  upon  our  earth, 
plants  and  animals  have  been  undergoing  changes,  is  called  evolu- 
tion. Man,  himself,  has  developed  according  to  the  laws  of  evolu- 
tion. 

Not  only  have  living  things  changed,  but  some  have  entirely 
disappeared  from  the  earth.  Thus,  there  are  no  longer  any  rep- 
tiles with  wings  or  great  monsters  that  can  browse  from  trees. 
Even  within  a  comparatively  few  years  buffaloes  and  wild  pi- 
geons have  practically  disappeared  from  North  America.  One 
of  the  most  remarkable  facts  related  to  this  changing  life  upon 
the  earth  is  that  man  by  making  use  of  certain  laws  of  nature  is 


374  THE  WORK  OF  THE  WORLD 

able  to  alter  and  improve  forms  of  life.  Thus,  our  ancestors 
never  knew  about  seedless  oranges,  corn,  tomatoes,  and  many 
other  kinds  of  plants,  as  well  as  animals,  which  to-day  are  quite 
common. 

In  this  project  it  will  be  our  purpose  to  learn  a  little  about 
how  living  things  come  into  existence  and  about  the  laws  of 
evolution,  especially  those  laws  which  govern  the  changes  di- 
rected by  man  for  his  own  benefit. 

PROBLEMS 
PROBLEM  i :  WHAT  ARE  THE  PARTS  OF  A  FLOWER? 

Directions: 

Take  any  large  flower,  such  as  the  tulip  in  the  spring  and  the  gladiolus 
in  the  fall,  for  purposes  of  study.  The  parts  of  the  flower  are  arranged  in 
circles  on  the  end  of  the  stem.  By  using  the  diagram  on  page  378,  see  if 
you  can  identify  the  sepals,  petals,  stamens,  and  pistil. 

Drawings: 

Make  a  diagram  to  show  the  number  and  relative  position  of  the  differ- 
ent parts  of  the  flower  you  are  studying.  Make  separate  drawings  of  the 
stamen  and  the  pistil.  In  the  former  drawing,  label  the  filament,  anther, 
and  pollen.  In  the  latter  drawing,  label  stigma,  style,  and  ovary.  Cut 
open  the  ovary  of  one  of  the  older  flowers.  What  do  you  find  inside? 
Draw  and  label. 

PROBLEM  2:  To  GROW  POLLEN  TUBES  AND  EXAMINE  THEM  UNDER  THE 

MICROSCOPE. 
Directions: 

Make  sugar  solutions  of  about  three,  ten,  and  fifteen  per  cent.  Shake 
some  ripe  pollen  from  different  flowers,  if  possible,  into  these  solutions. 
Place  a  drop  from  each  of  these  solutions  separately  upon  several  slides  and 
keep  in  a  moist  chamber  for  about  twenty-four  hours.  Then  examine 
under  a  microscope.  Look  for  prolongations  or  root-like  processes  ex- 
tending out  from  the  pollen  grains. 

Drawings: 

Draw  some  of  the  pollen  grains  with  and  without  pollen  tubes. 

PROBLEM  3 :  How  DOES  A  FRUIT  DEVELOP? 
Directions: 

Use  apples  or  bean  and  pea  pods.  Find  the  part  of  the  fruit  that  was 
attached  to  the  parent  plant.  See  if  any  parts  of  the  sepals,  stamens, 
stigma,  and  style  are  left.  What  do  you  notice  about  the  positions  of  these 


LIFE —ITS  ORIGIN  AND  BETTERMENT    375 

parts  with  reference  to  the  fruit  as  a  whole?    What  part  of  the  flower  does 
this  indicate  that  the  fruit  itself  has  come  from? 

If  possible,  examine  old  flowers  to  see  the  early  development  of  the  fruit. 
Compare  the  young  fruit  with  the  ripened  fruit.  Determine  the  position 
of  the  seeds.  Are  they  attached  to  the  fruit?  For  what  purpose? 

Question: 
Why  does  a  rainy  May  often  cause  a  poor  apple  crop? 

PROBLEM  4:  To  TAKE  A  FIELD  TRIP  TO  OBSERVE  (i)  CROSS- POLLINA- 
TION AND  (2)  THE  STRUGGLE  FOR  EXISTENCE. 
Directions: 

Part  I.  Cross-pollination. 

If  possible,  visit  an  apple  orchard  during  apple-blossom  time.  Can  you 
see  the  bees  flying  about  from  one  blossom  to  another?  What  are  they 
after?  Incidentally  what  are  they  doing  that  is  of  use  to  us  and  to  tke 
plant  world  as  well? 

If  you  cannot  visit  an  apple  orchard,  go  out  into  the  fields  and  observe 
the  actions  of  the  insects,  especially  bees  and  butterflies.  Try  to  follow  a 
bee  as  it  goes  from  flower  to  flower.  Notice  whether  different  kinds  of 
flowers  are  visited  or  whether  flowers  of  only  one  kind  are  sought  for.  See 
if  you  can  find  any  flower  that  is  peculiarly  fitted  or  adapted  by  its  shape 
for  cross-pollination.  Explain.  Of  what  use  are  the  prettily  colored  parts 
of  flowers? 

Part  2.  The  struggle  for  existence. 

Can  you  observe  any  facts  relating  to  the  habits  and  manner  of  living 
of  the  animals  and  plants  of  the  field,  pond,  or  woods  that  would  indicate 
on  the  one  hand  that  they  have  enemies  and  on  the  other  hand  that  they, 
themselves,  prey  upon  other  living  things?  Consider  the  insects,  spiders, 
water  animals,  field  mice,  and  birds,  especially.  Of  what  use  is  it  for  the 
spider  to  spin  its  web,  insects  and  fish  to  lay  great  numbers  of  eggs,  field 
mice  to  live  under  ground,  birds  to  build  nests  in  trees  or  shrubs  and  little 
fish  to  stay  in  shallow  water? 

Regarding  the  trees  and  other  plants  of  the  woods  and  fields,  what  facts 
can  you  observe  that  would  seem  to  indicate  a  struggle  for  existence? 
What  facts  can  you  readily  observe  regarding  the  effects  of  the  struggle 
for  existence  especially  with  reference  to  the  appearance  of  trees  in  the 
woods  in  comparison  with  the  appearance  of  the  same  kind  of  trees  in  open 
places?  How  do  you  explain  these  facts? 

PROBLEM  5 :  To  DESTROY  FLIES  AND  MOSQUITOES. 

Directions: 

Part  I.  Getting  rid  of  mosquitoes. 

If  there  are  any  mosquitoes  in  your  neighborhood,  look  for  their  breed- 


376  THE  WORK  OF  THE  WORLD 

ing-places.  Mosquitoes  are  apt  to  breed  wherever  there  is  standing  water, 
such  as  may  be  found  in  barrels,  tin  cans,  or  other  small  receptacles. 
Remove  such  breeding-places.  If  there  are  large  bodies  of  standing  water, 
pouring  oil  over  the  surface  will  destroy  any  young  mosquitoes  that  may 
be  in  the  water.  Draining  swamps  is  even  a  better  method. 

Part  2.  Getting  rid  of  flies. 

If  there  are  any  flies  in  your  neighborhood,  try  to  find  their  breeding- 
places  and  have  them  removed  or  properly  screened  or  otherwise  protected 
against  the  possibility  of  flies  laying  their  eggs  there.  If  you  live  in  a  city, 
uncovered  manure  piles  should  be  reported  to  the  authorities.  If  you  live 
in  the  country  you  can  see  to  it  that  manure  piles  are  covered  and  that 
garbage  is  either  buried' or  burned. 

PROBLEM  6:  How  CAN  I  IMPROVE  MY  OWN  ENVIRONMENT? 

Directions  : 

The  problem  may  be  divided  into  four  parts:  (i)  my  personal  or  immedi- 
ate surroundings;  (2)  my  home  life;  (3)  my  school  life;  (4)  my  community 
life.  This  problem  need  not  be  reported  upon  in  class  but  should  be  given 
careful  attention  by  all.  It  is  meant  to  deal  with  the  factors  in  my  envi- 
ronment which  I  am  able,  to  a  considerable  extent  at  least,  to  control. 

(1)  My  personal  or  immediate  surroundings:  Do  I  keep  my  mouth,  teeth, 
skin,  and  clothing  clean?    Am  I  careful  about  my  personal  habits  regarding 
eating,  drinking,  and  attending  to  other  needs? 

(2)  My  home  life:  What  am  I  doing  to  help  make  my  home  a  pleasant 
and  healthful  place  in  which  to  live?    Can  I  help  to  keep  it  clean,  properly 
warmed,  ventilated,  and  otherwise  in  good  condition?     Am  I  doing  my 
share  toward  these  ends?     Just  what  am  I  doing? 

(3)  My  school  life:  Am  I  helping  to  make  my  school  environment  pleasant 
and  healthful?     If  so,  how? 

(4)  My  community  life:  Are  there  any  objectionable  things  in  my  neigh- 
borhood, such  as  flies,  mosquitoes,  dirty  places,  etc.?    If  so,  what  can  I  do 
to  remedy  these  conditions?     What  is  the  condition  of  the  streets,  trees, 
and  stores  in  my  vicinity?     Have  I  ever  written  to  the  Board  of  Health 
or  other  authorities  that  might  have  some  means  of  remedying  dangerous 
or  undesirable  conditions? 

Conclusion: 

What  conclusions  can  I  justifiably  make  regarding  the  following  points: 
(i)  Is  my  environment  perfect,  excellent,  good,  poor,  or  bad?  (2)  Can  I  do 
anything  to  improve  it?  (3)  Am  I  doing  very  much,  a  fair  amount,  or  only 
a  little  to  make  it  better?  (4)  Is  it  worth  while  to  make  the  effort  to  do 
more?  (5)  Will  I  make  this  effort  and  begin  at  once? 

All  life  comes  from  life.  We  have  already  found  that  one  way 
of  grouping  objects  in  our  world  is  to  divide  them  into  three 


LIFE  —  ITS  ORIGIN  AND  BETTERMENT    377 

classes:  solids,  liquids,  and  gases.  Another  way  of  classifying 
the  objects  around  us  is  to  group  them  as  living  and  non-living 
things.  The  study  of  living  things  is  called  biology. 

One  of  the  great  questions  that  has  interested  biologists  has 
been  the  origin  of  life.  Before  Pasteur  performed  certain  experi- 
ments which  proved  that  living  things  could  originate  only  from 
other  living  things  of  the  same  kind,  it  was  believed  by  many 
reputable  scientists  that  some  of  the  lower  forms  of  life  could 
spring  into  existence  directly  from  foods.  This  was  known  as  the 
theory  of  spontaneous  generation.  Many  learned  men  formerly 
believed  in  this  theory  because  otherwise  they  could  not  explain 
the  presence  of  certain  growths  in  some  kinds  of  foods.  Pasteur 
showed  that  living  things  would  not  grow  in  foods  that  had  been 
sterilized  and  then  kept  from  the  outside  air.  He  showed  that  the 
reason  they  start  to  grow  upon  foods  is  because  the  air  contains 
very  small,  invisible  spores  or  seed-like  bodies  —  living  organisms 
—  which,  when  they  fall  upon  exposed  foods,  start  to  grow  and 
multiply  very  rapidly  under  favorable  conditions.  In  other  words, 
he  proved  that  cells  can  come  only  from  cells. 

Methods  of  reproduction.  Reference  has  already  been  made 
several  times  to  one  method  of  reproduction,  the  kind  which  is 
found  in  the  lowest  forms  of  plants  and  animals  where  the  cell 
simply  divides  in  two.  This  sort  of  reproduction  not  only  occurs 
among  the  simplest  living  things,  but  it  is  in  this  manner  also  that 
the  cells  of  the  higher  forms  of  life  divide.  Thus,  the  cells  in  the 
trunk  of  a  tree  by  dividing  and  growing  will  result  in  the  growth 
of  the  tree.  This,  however,  does  not  result  in  producing  a  new 
tree.  It  only  results  in  growth.  If  a  new  tree  is  to  be  produced 
a  different  process  must  take  place.  What  is  true  of  a  tree  is 
likewise  true  of  a  baby  or  any  other  living  thing  composed  of  a 
great  number  of  cells. 

Just  as  it  is  true  that  among  the  lowest  forms  of  plants  and 
animals  their  methods  of  reproduction  are  similar,  it  is  also  true 
that  among  the  higher  forms  of  living  things,  whether  plants  or 
animals,  the  fundamental  steps  in  this  process  are  alike. 

Seeds  and  eggs.  What  do  you  suppose  a  seed  must  contain  in 
order  that  a  young  plant  may  come  from  it?  Naturally  one  would 


378 


THE  WORK  OF  THE  WORLD 


say  a  baby  plant,  and  this  is  true.  Along  with  the  baby  plant 
there  is  a  food  supply  to  help  the  plant  grow.  Eggs  in  the  ani- 
mal kingdom  correspond  to  seeds  in  the  plant  kingdom.  In- 
sects, frogs,  toads,  snakes,  fishes,  birds,  and  all  the  higher  forms 
of  life  come  from  eggs. 

Let  us  inquire  a  little  more  deeply  into  the  origin  of  living 
things  and  find  out  as  exactly  as  possible  how  seeds  come  into 
existence.  This  will  involve  the  study  of  flowers,  their  parts, 
and  how  they  work  together. 

A  baby  plant  in  the  making.  Seeds  come  from  flowers.  After 
the  flower  withers  and  some  of  its  parts  fall  off,  there  ordinarily 
remains  a  certain  part  which  grows  into  the  fruit.  The  fruit  con- 
tains the  seeds.  When  the  word  fruit  is  mentioned,  most  of  us 

probably  think  of  such  things 
as  apples,  pears,  and  peaches. 
It  may  surprise  you  to  know 
that  a  string-bean,  a  tomato, 
and  a  grain  of  corn  are  also 
fruits.  All  fruits  are  formed  in 
the  central  parts  of  flowers.  At 
first  they  are  very  small,  but 
after  continuing  to  receive 
nourishment  for  an  extended 
period  of  time  from  the  parent 
plant,  they  finally  grow  into 
fruits. 

The  parts  of  a  flower  and 
their  work.     Most  people  are 
attracted    by    the    beauty    of 
We  know  that  they 
many  different  sizes,  col- 
In   spite   of 

the  fact  that  there  are  so  many 
different  kinds  of  flowers,  it  is  nevertheless  true  that  all  perfect 
flowers  are  alike  in  having  the  same  kind  of  parts.  If  we  learn 
about  the  structure  of  a  typical  flower,  we  shall  at  the  same 
time  obtain  information  about  all  kinds  of  flowers. 


FIG.  196.    The  parts  of  a  flower.     Se,  se-    flowers 
pals;  Pe,  petals;  Pi,  pistil;  St,  stamens.    The 
of  a,  the  anther,  and  /, 


the  filament.    The  parts  of  the  pistil  are,  st,    ors     ancj    shapes, 
the  stigma;  sty,  the  style;  and  o,  the  ovary. 


LIFE  —  ITS  ORIGIN  AND  BETTERMENT    379 

(1)  Petals  and  sepals.     If  you  examine  most  flowers,  you  will 
find  that  there  are  showy,  prettily  colored  portions  and  that 
around  these  parts  there  are  smaller,  green  structures  which  look 
something  like  leaves.     The  gayly  colored  parts  are  called  petals 
and  the  green  parts  are  the  sepals.     None  of  these  structures  is 
actively  engaged  in  helping  to  make  seeds,  although  in  many  cases 
without  the  petals  no  seeds  would  be  formed,  since  they  attract 
to  the  flowers  insects  which,  as  will  be  explained  later,  are  some- 
times necessary  for  the  production  of  seeds.     The  sepals  protect 
the  flower,  especially  when  young  or  in  the  bud. 

(2)  The  pistil.     The  parts  of  the  flower  that  are  actively  en- 
gaged in  making  seeds,  that  is,  in  forming  baby  plants,  are  en- 
closed by  the  petals.     If  the  flower  is  a  perfect  one,  that  is,  if  it 
has  all  the  parts  —  as  most  flowers  have  —  there  can  be  found  in 
the  center  a  structure  called  a  pistil.    This  is  usually  shaped  some- 
thing like  a  vase  or  Indian  club.     The  lower,  swollen  portion, 
called  the  ovary,  is  where  the  seeds  under  proper  conditions  will 
develop.     In  very  young  flowers  the  ovaries  contain  microscopic 
structures,  called  egg-cells,  from  which  the  baby  plants  come,  but 
egg-cells  by  themselves  cannot  develop  into  plants.     They  need 
help  to  do  this.     There  is  another  part  of  the  flower  which  we 
have  not  yet  studied,  which  cooperates  with  them. 

(j)  The  stamens.  Encircling  the  pistil  there  are  usually  several 
upright  structures.  These  are  the  stamens,  the  swollen  ends  of 
which  at  certain  seasons  contain  a  powdery  substance  which  is 
the  pollen.  The  swollen  ends  are  called  anthers.  The  work  of 
the  stamens  is  to  make  pollen  grains,  just  as  the  main  work  of 
the  pistil  is  to  produce  egg-cells. 

How  a  part  of  the  pollen  grain  reaches  the  egg-cell.  In  order 
that  an  egg-cell  may  develop  into  a  baby  plant  it  is  necessary 
that  a  part  of  the  pollen  grain  should  unite  with  a  part  of  the  egg- 
cell.  At  first  it  might  seem  that  this  cannot  happen,  because  egg- 
cells  ara  deep  within  the  ovary  of  the  pistil  and  nothing  from 
outside  can  touch  them.  Nature,  however,  has  developed  a  won- 
derful means  whereby  the  part  of  the  pollen  grain  that  is  neces- 
sary can  reach  the  egg-cell  and  fertilize  it;  that  is,  unite  with  it 
and  make  it  possible  for  a  new  living  thing  to  be  produced. 


380 


THE  WORK  OF  THE  WORLD 


On  the  very  tip  of  the  pistil  there  is  a  part,  called  the  stigma, 
which,  when  ripe,  has  a  sticky  surface.  Some  pollen  grains  from 
the  same  flower  or  from  other  flowers  of 
the  same  kind  fall  upon  this  sticky  sub- 
stance. They  then  absorb  some  of  the 
sweet  fluid  that  they  find  there  and,  burst- 
ing open,  send  out  a  root-like  projection  of 
living  matter.  This  projection  is  called 
a  pollen  tube.  It  contains  the  part  of 
the  pollen  grain  that  is  needed  to  help 
"awaken"  the  egg-cell  and  start  it  grow- 
ing into  a  baby  plant.  The  pollen  tube 
or  projection  grows  down  from  the  stigma, 
through  the  style,  as  the  neck  of  the  pistil 
is  called,  until  it  reaches  that  part  of  the 
pistil  where  the  egg-cells  are  located. 
Usually  many  pollen  tubes  are  growing 
down  into  the  ovary  at  the  same  time. 
The  first  ones  to  reach  the  egg-cells  dis- 
charge part  of  their  contents  into  them. 
A  union  of  parts  thus  accomplishes  the 
most  essential  step  in  this  whole  process. 
This  uniting  process  is  called  fertilization.  One  pollen  tube  is 
necessary  to  fertilize  one  egg-cell. 

Development  of  the  fertilized  egg.  The  egg  after  it  has  re- 
ceived part  of  the  pollen  grain  soon  becomes  active  and  by  grow- 
ing and  dividing  into  many  cells  it  eventually  makes  a  baby  plant. 
At  this  stage  it  must  receive  nourishment  from  the  parent  plant, 
if  it  is  to  develop  properly.  It  is  therefore  attached  to  the  parent 
plant  to  receive  this  nourishment.  Some  of  the  food  which  is 
being  made  in  the  leaves  is  transported  to  the  young  plants  in 
the  developing  seeds. 

Summary  of  the  steps  in  the  development  of  a  seed.  Before  a 
seed  can  be  produced,  the  'following  conditions  are  necessary: 
(i)  There  must  be  produced  two  kinds  of  cells  in  the  reproductive 
organs  of  a  flower,  the  stamens  producing  pollen  grains  and  the 
pistil,  egg-cells.  (2)  A  pollen  grain  must  fall  upon  the  stigma  of 


FIG.  197.  Pollen  grains, 
highly  magnified.  A,  pink; 
B,  nasturtium,  the  pollen 
grain  has  taken  in  food  and 
formed  a  tube;  C,  pumpkin, 
with  tube;  D,  contents  of 
grain  passing  down  tube. 


LIFE  —  ITS  ORIGIN  AND  BETTERMENT    381 


the  pistil.  This  act  is  known  as  pollination. 
(3)  The  pollen  grain  must  germinate  and  send 
out  a  prolongation  containing  the  pollen  grain 
cell.  This  makes  its  way  down  the  style  and 
into  the  ovary,  eventually  reaching  the  egg-cell 
and  a  union  of  cells  takes 
place.  This  process  is 
known  as  fertilization. 
(4)  As  a  result  of  fertiliza- 
tion, the  egg-cell  begins  to 
divide  into  a  great  num- 
ber of  cells.  Finally,  pro- 
viding it  continues  to  re- 
ceive nourishment  from  the 
parent  plant,  it  grows  into 
a  baby  plant. 

Reproduction  in  higher 
forms    of    animals.      The 
reproduction    of    all    the 
higher  forms  of  both  plants 
FIG.  198.    Fertilization  in    an(j  animals  has  strikingly 

a  pistil.    The  pollen  grain,        ...  .  ,, 

p,  sends  a  tube,  /,  down  to    similar  points  to  the  proc- 

the  ovary,  o,  where  it  reaches     ess    jus|-    described.      That 
an  egg-cell,  e.  .  .  .. 

is  to  say,  when  a  new  liv- 
ing being  is  to  be  produced  it  is  necessary  for 
two  cells  to  unite.  The  fertilized  egg  then  be- 
gins to  develop  and  under  favorable  conditions 
eventually  forms  a  new  plant  or  animal,  as  the 
case  may  be.  Thus,  in  the  reproduction  of 
many  kinds  of  fishes,  the  female  lays  the  eggs  in 
shallow  water.  The  male  fish  deposits  a  sub- 
stance, called  milt,  over  them.  Milt  consists  of 
cells  which  correspond  to  the  pollen  grain  cells  in 
flowers.  These  cells  move  toward  and  unite  with 
the  egg-cells,  causing  their  fertilization.  The 
egg-cell  then  begins  to  develop  into  a  baby  fish. 
Kinds  of  pollination.  Returning  to  the  subject 


FIG.  199.  The 
fruit  of  a  bean  plant 
which  is  a  developed 
ovary  and  the  at- 
tached parts,  S,  re- 
mains of  the  sepals; 
St,  the  dried-up  stig- 
ma and  style.  The 
pod  is  the  enlarged 
ovary  containing,  B, 
the  beans  or  seeds 
attached  to  the  wall 
of  the  ovary. 


382  THE  WORK  OF  THE  WORLD 

of  seed  formation,  we  notice  that  the  falling  of  the  pollen  upon 
the  stigma  is  called  pollination.  Possibly  you  have  been  won- 
dering how  the  pollen  grains  pass  from  the  anthers  of  the  stamens 
to  the  stigmas  of  the  pistils.  It  is  true  that  although  usually 
enough  pollen  grains  fall  upon  the  stigmas  to  fertilize  all  the  egg- 
cells,  many  pollen  grains  never  reach  their  destination.  This  is  due 
to  the  fact  that  it  is  often  necessary  for  the  pollen  to  be  carried  from 
a  considerable  distance  before  it  reaches  the  stigmas.  You  will 
understand  this  better  when  you  realize  the  following  conditions : 
(i)  Some  plants  have  flowers  which  have  no  stamens  and  other 
plants  have  flowers  with  no  pistils.  (2)  In  some  plants  the  pollen 
grains  and  pistils  ripen  at  different  times  so  that  when  the  stigmas 
are  ready  to  receive  pollen,  either  the  pollen  grains  of  that  par- 
ticular flower  have  disappeared  or  else  they  are  not  ripe.  In 
either  event  the  pollen  grains  must  be  brought  from  another 
flower.  (3)  Again,  there  are  some  flowers  in  which  the  egg-cells 
and  pollen  grains  are  not  able  to  unite  although  ripening  at  the 
same  time.  In  such  cases  also  there  is  need  for  the  pollen  to  come 
from  other  flowers.  Even  in  those  flowers  where  the  pollen  grains 
may  fertilize  the  egg-cells  of  the  same  flower,  much  of  the  pollen 
is  usually  blown  away  and  eventually  falls  to  the  ground  where, 
of  course,  it  is  of  no  use. 

From  these  facts  it  can  readily  be  seen  that  it  is  necessary  for 
the  flowers  of  most  plants  to  make  many  more  pollen  grains  than 
egg-cells  in  order  to  make  pollination  and  fertilization  assured. 
It  is  not  unusual  for  plants  to  produce  thousands  of  pollen  grains 
to  every  egg-cell.  Thus,  if  you  were  to  go  into  the  pine  woods 
at  the  time  the  flowers  are  in  bloom  upon  the  pine  trees,  you 
could  see  that  as  the  wind  shook  the  trees  and  the  pollen  dust  was 
blown  off,  the  air  would  actually  become  yellow  with  the  great 
numbers  of  pollen  grains.  Comparatively  only  a  few  of  these 
would  ever  reach  the  places  where  they  could  accomplish  the 
work  for  which  they  were  made. 

From  facts  already  given  it  can  readily  be  seen  that  pollen 
grains  may  (i)  fall  upon  the  stigma  of  the  same  flower  in  which 
they  were  made;  or  (2)  upon  the  stigmas  of  other  flowers  of  the 
same  kind.  The  first  kind  of  pollination  is  called  self-pollination; 
the  second,  cross-pollination. 


LIFE  —  ITS  ORIGIN  AND  BETTERMENT    383 

How  cross-pollination  is  accomplished.  There  are  two  com- 
mon methods  by  which  cross-pollination  is  accomplished:  (i)  The 
wind  may  carry  the  pollen.  (2)  Insects  may  act  as  the  carriers. 
Many  insects  are  peculiarly  adapted  or  fitted  to  transfer  pollen 
from  flower  to  flower.  The  bee  is  an  insect  of  this  kind.  With- 
out the  work  of  bees  we  should  have  no  apples,  since  the  cross- 
pollination  of  apple-blossoms  depends  upon  these  insects.  Bees 
also  cross-pollinate  many  other  kinds  of  flowers.  Insects  visit 
flowers  to  obtain  the  sweet  juice  or  nectar  which  the  flowers 
hold.  To  obtain  this  juice  the  insects  must  necessarily  rub  against 
the  anthers  and  stigmas.  When  they  visit  another  flower  some 
of  the  pollen  which  they  obtained  from  the  anthers  is  rubbed  off 
upon  the  stigmas.  In  this  manner  cross-pollination  occurs. 

Artificial  cross-pollination.  By  the  term  artificial  cross-pollina- 
tion is  meant  the  transference  of  pollen  from  one  flower  to  an- 
other by  man.  A  camel's-hair  brush  is  often  used.  The  flower 
that  is  to  receive  the  pollen  is  stripped  of  its  own  stamens  before 
the  stigmas  are  ripe.  It  is  then  covered  with  a  bag  so  as  to  pre- 
vent any  pollen  from  outside  falling  upon  the  stigma.  At  the 
time  the  stigma  is  ripe  pollen  grains  are  placed  upon  it.  By  this 
means  Luther  Burbank  and  others  have  been  able  to  produce 
new  varieties  of  plants  and  improve  old  ones.  The  principle 
involved  is  not  difficult  to  understand,  when  you  have  learned 
about  the  nature  of  pollen  grains  and  egg-cells. 

The  meaning  of  heredity.  You  know  that  both  plants  and 
animals  can  produce  other  living  things  of  a  kind  similar  to 
themselves.  The  continuance  from  generation  to  generation  of 
similar  traits  is  known  as  heredity.  Thus,  one  kind  of  flower 
can  produce  seeds  that  have  the  power  of  developing  into  only 
one  kind  of  plant  —  a  plant  similar  to  that  of  which  the  flow- 
ers formed  a  part.  Further,  it  has  been  found  that  the  reason 
for  this  fact  is  that  the  egg-cell  and  the  pollen  grain  cell  have 
within  them  certain  structures  which  carry  the  traits  or  charac- 
teristics from  parent  to  offspring.  The  same  general  facts  are 
true  among  animals.  All  the  higher  forms  of  animals  have  come 
into  existence  as  a  result  of  the  union  of  two  cells,  one  from  each 
parent.  These  cells,  as  in  the  case  of  the  pollen  and  egg  cells  of 


384  THE  WORK  OF  THE  WORLD 

plants,  carry  the  materials  in  them  which  determine  the  kind  of 
offspring  that  is  to  be  formed. 

The  meaning  of  variation.  From  what  has  been  said  so  far  it 
might  be  supposed  that  living  beings  would  be  exactly  like  their 
parents.  If  this  were  the  case,  all  the  children  in  any  family 
would  all  be  the  same.  We  know  that  this  is  not  true.  They 
may  differ  very  markedly  from  each  other.  In  fact  it  is  impos- 
sible to  find  any  two  individuals  that  are  just  alike.  The  same 
fact  is  true  of  other  living  things.  This  difference  existing  be- 
tween living  things  is  called  variation. 

Charles  Darwin  and  evolution.  Charles  Darwin  in  one  of 
the  world's  greatest  books,  called  the  Origin  of  Species,  brought 
forward  facts  which  clearly  indicated  that  living  beings  have 
evolved  or  changed  during  their  existence  upon  the  earth.  One 
of  the  explanations  which  Darwin  advanced  as  to  the  cause  of 
these  changes  is  known  as  the  "survival  of  the  fittest."  No  one 
can  study  the  conditions  existing  in  a  natural  forest  or  in  a  field 
without  being  impressed  with  the  keen  struggle  for  existence  that 
is  going  on  among  the  living  things  in  it.  Most  of  the  seeds 
which  are  produced  never  have  the  opportunity  of  germinating, 
and  of  those  that  do  germinate  the  majority  are  killed  off  before 
they  become  mature  or  full-grown.  Only  a  very  small  percentage 
of  them  ever  reach  a  condition  where  they  themselves  are  able 
to  produce  seeds.  A  similar  condition  is  true  among  animals. 
Certain  varieties  of  fish  lay  millions  of  eggs,  but  only  a  compara- 
tively few  ever  develop  into  fish.  Many  of  the  eggs  are  eaten 
by  other  fish  before  they  hatch  or  after  hatching  the  young  fish 
are  devoured  in  great  numbers  by  larger  fish.  . 

Even  among  men  there  is  a  great  struggle  for  existence.  The 
majority  of  people  are  not  what  could  be  called  successful  indi- 
viduals. Great  numbers  of  babies  die  because  of  lack  of  proper 
care  and  many  lives  are  lost  through  sicknesses  that  result  from 
this  struggle  for  existence.  Darwin  reasoned  that  in  most  cases  the 
strongest  would  survive  and  pass  on  their  characteristics  to  their 
offspring.  There  is  a  tendency  for  the  weaker  forms  to  perish. 

The  meaning  of  selection.  Plant  and  animal  breeders  by  study- 
ing groups  or  varieties  of  plants  and  animals  and  observing  their 


LIFE  —  ITS  ORIGIN  AND  BETTERMENT    385 


strong  and  weak  points  have  been  able  by  crossing  certain  ones  to 
develop  new  varieties  that  have  a  new  combination  of  desirable 
characteristics.  Thus,  Luther  Burbank  has  developed  new  forms 
of  plants  that  are  more  desirable  than  previously  existing  forms. 
He  has,  for  example,  been  able  to  produce  more  beautiful  flowers 
and  to  grow  fruits  of  more 
delicious  flavor.  He  has  been 
able  to  do  this  by  applying 
the  principles  of  heredity  and 
variation,  especially  by  carry- 
ing out  experiments  in  cross- 
pollination. 

Let  us  take  a  specific  exam- 
ple. Let  us  suppose  that  it  is 
desired  to  obtain  seeds  which 
will  develop  into  trees  that 
bear  early  luscious  cherries. 
Let  us  suppose  that  we  have 
cherry  trees  which  bear  early, 
but  yield  sour  cherries,  and 
that  we  also  have  trees  which 
produce  luscious  cherries  rath- 
er late  in  the  season.  By  arti- 
ficially cross-pollinating  the 
flowers'  of  these  trees,  it  may 
be  possible  to  obtain  some 
seeds  which  have  the  desirable 
characteristics  of  both. 

After  obtaining  seeds  as  a 
result  of  artificial  cross-pollin- 
ation and  planting  them,  the  new  desired  characteristics  may  not 
show  in  the  next  generation,  or  if  they  do  appear,  they  may  be 
found  in  only  a  few  forms.  Again,  some  of  the  new  forms  may 
show  combinations  of  undesirable  traits.  It,  therefore,  imme- 
diately becomes  necessary  to  select  the  best  and  reject  the 
others.  ,  This  is  what  is  meant  by  selection.  Luther  Burbank 
rejects  many  more  plants  than  he  selects,  and  sometimes  he  has 


FIG.  200.  The  spineless  cactus,  one  of  Luther 
Burbank's  improved  plants.  Without  the 
prickly  spines,  cactus  plants  have  proved  val- 
uable food  for  cattle. 

(Courtesy,  Luther  Burbank.) 


386  THE  WORK  OF  THE  WORLD 

to  work  a  long  time  before  he  obtains  that  for  which  he  is 
seeking. 

Long  before  the  time  of  Luther  Burbank  this  selective  process 
was  being  carried  on  by  the  men  who  raised  animals  and  culti- 
vated the  fields.  The  methods  of  plant  and  animal  breeders  of 
to-day  differ  from  the  old  methods  in  that  they  are  carried  on 
more  extensively  and  intelligently  because  of  a  greater  knowledge 
of  the  natural  laws  involved.  Even  before  men  began  to  select 
those  plants  and  animals  that  they  wished  to  cultivate  or  domes- 
ticate, a  selective  process  was  being  carried  on  by  nature.  This 
was  an  inevitable  result  of  the  struggle  for  existence  to  which 
reference  has  already  been  made.  This  kind  of  selection  is  called 
natural  selection  to  distinguish  it  from  man's  selection,  which  is 
called  artificial  selection. 

Improving  living  conditions.  When  we  compare  the  conditions 
in  the  home  and  community  under  which  we  live  to-day  with  the 
conditions  existing  in  the  time  of  our  great-grandparents,  it  can 
readily  be  seen  that  great  advances  have  been  made.  Health  is 
safeguarded  much  more  thoroughly  now  than  it  was  fifty  or  one 
hundred  years  ago.  We  have  studied  how,  for  example,  water- 
and  food-supplies  are  protected  and  how  wastes  are  disposed  of 
so  as  not  to  spread  disease.  Great  strides  have  been  made  in 
these  lines  during  recent  years.  The  one  great  factor  which  has 
made  this  advance  possible  has  been  the  rise  of  the  science  of 
bacteriology.  This  subject  has  opened  a  new  field  of  knowledge 
concerning  the  cause  and  manner  of  spreading  of  some  of  the 
most  common  diseases.  As  a  result  it  has  been  possible  to  fight 
them  more  effectively. 

Preventive  medicine.  Bacteriology  has  made  possible  preven- 
tive medicine,  a  term  that  is  applied  to  treatment  used  to  prevent 
disease,  rather  than  curing  it.  The  old  saying,  "An  ounce  of 
prevention  is  worth  a  pound  of  cure,"  has  no  better  application 
than  to  disease.  The  use  of  diphtheria  antitoxin  is  one  example 
where  preventive  medicine  is  employed.  (See  page  60.)  Other 
well-known  examples  where  preventive  measures  are  employed 
to  avoid  the  contraction  of  disease  are  inoculation  against  Jyphoid 
fever  and  vaccination  against  smallpox. 


LIFE— ITS  ORIGIN  AND  BETTERMENT    387 

Vaccination  against  smallpox.  In  the  early  part  of  the  nineteenth  cen- 
tury Jenneiv  an  English  physician,  first  extensively  used  the  method  of 
vaccination  against  smallpox  that  is  now  almost  universally  employed. 
At  the  time  this  treatment  was  first  used  the  principle  underlying  its  oper- 
ation was  not  understood.  It  was  more  than  half  a  century  later  that 
Pasteur  demonstrated  that  it  is  possible  to  prevent  the  occurrence  of  some 
diseases  by  actually  putting  into  the  body  the  weakened  bacteria  or  other 
agents  capable  of  producing  a  mild  form  of  the  disease.  The  placing  of 
these  organisms  in  the  body  either  alive  or  dead  is  called  inoculation. 
The  most  common  method  is  where  they  are  injected  under  the  skin.  In 
the  case  of  smallpox  the  organisms  injected  are  known  as  cow-pox  germs. 
They  are  related  to  the  organism  producing  smallpox,  probably  a  weakened 
form,  which  are  capable  of  doing  practically  no  harm  to  the  human  body. 
Yet  they  are  capable  of  so  affecting  the  body  that  it  develops  the  power 
not  only  of  fighting  against  the  cow-pox  germs  but  also  of  successfully 
combating  smallpox  organisms  if  any  should  happen  to  gain  an  entrance. 

There  is  nothing  more  striking  in  the  history  of  science  than  the  effects 
of  vaccination.  Wherever  it  has  been  universally  introduced,  there  small- 
pox has  been  almost,  if  not  completely,  prevented.  Before  the  custom  of 
vaccination  became  prevalent  nine  people  out  of  every  ten  who  reached  the 
age  of  thirty  were  pock-marked  —  that  is,  they  had  been  disfigured  by  the 
disease  —  and  about  one  person  out  of  every  ten  died  from  it.  In  many 
places  where  the  practice  of  vaccination  has  been  temporarily  abandoned, 
the  disease  has  again  shown  itself.  It  would  seem,  therefore,  that  the  only 
reason  that  smallpox  is  not  prevalent  to-day  is  because  the  practice  of 
vaccination  holds  it  in  check. 

Inoculation  against  typhoid  fever.  The  preventive  treatment  for  ty- 
phoid fever  that  is  so  extensively  used,  especially  in  armies,  consists  of 
inoculating  a  certain  quantity  of  dead  typhoid  bacilli  under  the  skin. 
Along  with  these  bacteria  there  is  a  quantity  of  the  poison  which  they 
produce  and  which  causes  the  disease.  Not  enough  of  this  is  injected, 
however,  to  do  any  serious  harm,  but  a  sufficient  amount  to  cause  the 
body  to  make  antibodies  which  will  be  present  to  prevent  the  contraction 
of  typhoid  fever  should  the  live  bacteria  gain  access  to  the  body.  The 
vaccination  against  typhoid  fever  usually  lasts  for  two  or  three  years;  while 
the  vaccination  against  smallpox  is  a  protection  usually  for  seven  years  or 
even  longer. 

Destroying  flies.  Flies  are  one  of  the  means  of  spreading  dis- 
ease. They  visit  filthy  places  and  then  are  apt  to  walk  over  our 
food  and  leave  a  trail  of  bacteria  wherever  they  go.  (See  page 
80.)  The  best  wTay  to  destroy  flies  is  to  give  them  no  place  in 
which  to  breed.  They  breed  in  filth  or  on  decaying  things.  The 


THE  WORK  OF  THE  WORLD 


female  lays  about  two  hundred  eggs.  These  hatch  in  a  few  days 
into  larvae,  called  maggots.  In  a  few  days  the  maggots  go  into 
a  resting  stage  and  shortly  emerge  into  adults,  the  whole  process 
from  egg  to  adult  taking  about  ten  days.  Two  favorite  breeding 
places  for  flies  are  manure  and  garbage  piles.  Manure  should 

be  kept  covered  and  gar- 

FLY 


LIFE   CYCLE   OF 


bage  should  be  disposed 
of  promptly  by  burning  or 
burying.  As  will  be  re- 
membered, flies  are  espe- 
cially apt  to  spread  ty- 
phoid fever;  in  fact,  the 
common  house-fly  is  often 
called  the  typhoid  fly. 

Destroying  mosquitoes. 
Mosquitoes  are  the  means 
of  spreading  two  diseases, 
malaria  and  yellow  fever. 
Malaria  is  spread  by  the 
female  of  a  certain  vari- 
ety of  mosquito,  called  the 
anopheles.  Yellow  fever  is 
spread  by  another  kind 
of  mosquito,  called  the 

stegomyia.  These  two  diseases  are  spread  in  very  much  the  same 
manner.  Therefore,  in  learning  about  one  of  them,  we  shall 
obtain  the  essential  features  regarding  the  other  also. 

Previous  to  1900  there  were  two  ideas  about  the  way  in  which  yellow 
fever  was  spread.  Some  authorities  thought  it  was  spread  by  mosquitoes, 
but  most  people  thought  it  was  spread  by  coming  into  contact  either  with 
the  sick  person  or  with  the  clothing  or  bedclothes  used  by  yellow-fever 
patients.  Under  the  direction  of  Dr.  Walter  Reed  experiments  were  con- 
ducted which  demonstrated  that,  it  was  never  spread  in  the  latter  way,  but 
always  by  the  bite  of  a  stegomyia  mosquito  which  had  previously  bitten  a 
person  sick  with  this  disease.  In  the  course  of  these  investigations,  a 
United  States  army  surgeon,  Dr.  Jesse  Lazear,  permitted  one  of  these  mos- 
quitoes to  bite  him.  He  became  sick  with  yellow  fever  and  died.  As  a 
result  of  this  and  certain  other  experiments  it  was  discovered  that  the  dis- 


FIG.  201.  Stages  in  the  life-history  of  a  fly. 
(Courtesy,  International  Harvester  Co.) 


LIFE— ITS  ORIGIN  AND  BETTERMENT    389 


DEATHS  FROM  DIARRHEAL  DISEASES 
GREATEST  IN  FLY  SEASON 


ease  is  spread  only  in  the  following  manner:  (i)  The  mosquito  is  never 
hatched  with  the  germ  of  the  disease  in  its  body  and  never  gets  it  in  any 
other  way  than  by  sucking  the  blood  of  a  yellow-fever  patient.  (2)  After 
the  mosquito  gets  the  germ  into  its  own  body,  it  is  able  in  a  little  less  than 
two  weeks  to  inject  some  of  the  germs  into  a  healthy  person. 

All  that  is  necessary  to  abolish  yellow  fever  is  to  destroy  mos- 
quitoes. By  pouring  oil  over  the  swamps  or  water  where  they 
breed,  it  is  possible  to  de- 
stroy the  mosquito  lar-  FLlCO 
V32,  or  wrigglers.  The  oil 
forms  a  film  over  the  sur- 
face of  the  water,  and 
when  the  wrigglers  try  to 
obtain  air  by  coming  to 
the  surface  they  are  un- 
able to  do  so,  and  are, 
therefore,  suffocated.  An- 
other way  of  destroy- 
ing mosquitoes  is  to  put 
into  the  water  fish  which 
eat  the  larvae.  An  even 
more  efficacious  way  of 
destroying  mosquitoes  is 
to  deprive  them  entirely 
of  their  breeding  places 


FIG.  202.  Flies  are  the  enemies  of  man. 
(Courtesy,  International  Harvester  Co.) 


by  draining   or   filling   in   swamps   and   by  not   allowing  any 
standing  water  to  remain  in  the  vicinity. 

The  mosquitoes  which  spread  malaria  breed  in  a  similar  manner  to  those 
causing  yellow  fever.  Malaria,  like  yellow  fever,  can  be  spread  only  by 
the  bite  of  a  mosquito.  The  malarial  mosquito,  like  the  stegomyia^  is 
never  hatched  with  the  disease  and  does  not  get  the  germ  in  swamps  or 
damp  places  but  must  obtain  it,  if  it  gets  it  at  all,  from  a  person  sick  with 
malaria.  It  was  formerly  thought  that  this  disease  was  spread  by  damp 
air,  since  it  was  very  prevalent  around  marshy  places.  In  order  to  inves- 
tigate this  point,  some  physicians  went  to  live  for  a  season  in  a  malaria- 
infested  district  in  the  marshes  around  Rome,  Italy,  where  the  air  is  very 
damp  and  where  malarial  mosquitoes  are  also  very  numerous.  These  in- 
vestigators screened  themselves  in,  only  going  out  during  the  day  when  it 


390  THE  WORK  OF  THE  WORLD 

was  safe  to  go  abroad,  since  the  anopheles  mosquitoes  do  not  fly  in  the  day- 
light. These  physicians,  although  being  in  the  midst  of  the  swamp,  where 
many  people  were  sick  with  malaria,  and  breathing  the  moist  night  air, 
did  not  contract  the  disease.  This  was  very  good  evidence  that  the  damp 
night  air  could  not  cause  the  disease.  Some  years  later  the  organism 
which  causes  the  disease  was  discovered  in  the  blood  of  patients  as  well 
as  in  the  bodies  of  mosquitoes. 


FIG.  203.  Destroying  mosquitoes  by  oiling  their  breeding  ground.   (From 
Hutchinson's  Handbook  of  Health.    Photograph  by  Paul  Thompson.) 

Improving  your  own  environment.  Probably  the  greatest 
thing  that  your  study  of  science  can  do  for  you  is  to  help  make  it 
possible  for  you  to  improve  your  own  environment  and  that  of 
the  people  around  you.  Look  for  some  of  the  ways  in  which  your 
environment  can  be  improved  and  then  work  for  these  improve- 
ments. If  you  will  do  this,  there  will  be  a  better  chance  not 
only  for  you,  yourself,  to  be  healthier  and  happier,  but  you  will 
also  help  make  the  world  better  for  other  people. 

INDIVIDUAL  PROJECTS 

Working  projects: 

Make  and  use  a  fly-trap. 
Directions  for  making  a  home-made  fly-trap.    International  Harvester  Co. 


LIFE  —  ITS  ORIGIN  AND  BETTERMENT    391 

Reports: 

1.  Luther  Burbank  and  his  work. 

Civic  Biology.     G.  W.  Hunter.    American  Book  Co. 

New  Creations  in  Plant  Life.     Harwood.     The  Macmillan  Co. 

2.  Preventing  disease. 

Handbook  of  Health.     W.  Hutchinson.     Houghton  Mifflin  Co. 

How  to  Live.     Fisher  and  Fisk.     Funk  &  Wagnalls. 

The  Human  Mechanism.     Hough  and  Sedgwick.     Ginn  &  Co. 

Pamphlets.     Metropolitan  Life  Insurance  Co. 

Primer  of  Sanitation.     J.  W.  Ritchie.     World  Book  Co. 

Town  and  City.     F.  G.  Jewett.     Ginn  &  Co. 

3.  Prehistoric  animals. 

Animals  of  the  Past.    F.  A.  Lucas.     McClure,  Phillips  &  Co. 

4.  House-flies. 

Farmers'  Bulletins  459  and  851.  U.S.  Department  of  Agriculture. 


SUGGESTIONS  TO  TEACHERS 

THIS  book  is  written  for  the  boys  and  girls  of  junior  high  school  age. 
The  authors  believe  that  directions  for  work  are  simple  and  clear  enough  to 
enable  the  children  to  obtain  good  results  in  scientific  habits  of  thought, 
careful  observation,  and  permanent  interest  in  science,  even  without  the 
aid  of  a  teacher.  Yet  the  life  of  every  course  is  the  teacher.  Some  sug- 
gestions are  herewith  included  which  have  helped  other  teachers. 

The  order  of  units.  The  units  are  interchangeable  in  order,  although, 
it  is  recommended  that  they  be  studied  in  the  order  suggested.  Part  I 
is  simpler  than  Part  II.  The  course  is  planned  to  occupy  two  years  in  the 
earlier  grades  of  the  junior  high  school  (grades  7  and  8),  or  one  year  in 
grade  9. 

The  problems.  Too  much  emphasis  cannot  be  placed  on  having  the 
problems  worked  out  before  any  text  on  the  subject  is  read.  Assign  the 
problems  first,  then  assign  the  reading. 

Committees  of  pupils  may  be  appointed  to  prepare  the  apparatus  for 
the  problems.  For  demonstration  or  class  experiments  especially,  such 
sharing  in  the  work  makes  the  pupils  feel  that  the  experiment  is  their  own, 
and  not  a  "show,  managed  by  the  teacher." 

A  classification  of  all  the  problems,  with  suggestions  for  assignments, 
is  found  on  pages  397  to  400. 

The  individual  projects.  Opportunity  should  be  given  for  much  indi- 
vidual and  group  activity  in  the  line  of  special  projects,  for  which  special 
credit  should  be  given.  The  projects  as  suggested  need  not  all  be  included ; 
current  events  will  determine  many,  local  conditions  others.  Each  pupil 
should  undertake  and  successfully  complete  at  least  one  or  two  projects 
during  the  course. 

Notebook.  It  is  recommended  that  every  pupil  keep  a  notebook,  con- 
taining a  description  of  some  of  the  problems  together  with  compositions, 
outlines,  and  drawings  treating  of  the  work  of  the  term.  It  is  unwise  to 
attempt  to  require  the  pupils  to  put  most  of  the  term's  work  into  the  note- 
book. Only  the  most  important  topics,  experiments,  and  reports  should  be 
so  treated.  It  is  better  to  concentrate  upon  a  few  things  and  have  them 
done  well  rather  than  to  attempt  too  much. 

In  writing  the  problems,  a  certain  amount  of  uniformity  is  desirable. 
The  following  plan  is  suggested: 

I.  Problem:  What  is  in  an  "Empty"  Glass? 

II.  Apparatus:  A  glass  and  a  basin  of  water.     (A  drawing  of  the  appa- 


394  SUGGESTIONS  TO  TEACHERS 

ratus,  especially  when  it  is  simple  as  in  this  case,  is  strongly  recommended, 
but  it  is  not  absolutely  essential.  The  pupils  should  be  made  to  understand 
that  neat  work,  including  careful  drawings,  will  receive  special  credit.) 

III.  Procedure:  I  inverted  the  glass  and  pressed  it  down  until  the  bot- 
tom was  below  the  surface  of  the  water,  being  careful  not  to  let  any  bub- 
bles escape. 

IV.  Result:  I  noted  that  it  required  a  little  force  to  press  the  glass  deep 
into  the  water  and  that  very  little  water  entered  into  the  glass. 

V.  Conclusion:  I  conclude  that  an  "empty"  glass  is  filled  with  air. 

VI.  Explanation:  If  the  glass  had  really  been  empty,  the  water  would 
have  entered  the  glass,  but  there  was  air  in  the  glass  and  this  kept  the 
water  out.    Air  is  a  real  substance  and  as  such  occupies  space. 

It  is  well  to  collect  the  notebooks  and  mark  them  early  in  the  term.  In 
this  way,  if  insistence  is  made  upon  having  the  work  accurate  and  neat, 
desirable  habits  will  be  formed.  The  notebooks  should  be  carefully  ex- 
amined and  marked  at  least  four  or  five  times  during  the  term.  Loose- 
leaf  notebooks  are  desirable,  in  order  that  reports  may  be  examined  as 
they  are  completed. 

The  following  method  of  marking  is  suggested : 

Work  done  on  time 15  per  cent 

Neatness 25  per  cent 

Accuracy 30  per  cent 

Completeness  of  statement 30  per  cent 

In  marking  the  notebooks,  correctness  of  statement  should  be  considered 
of  prime  importance.  Close  scrutiny  of  the  last  parts  of  the  problems  is 
needed  to  see  that  correct  conclusions  or  inferences,  and  explanation,  when 
needed,  are  made.  In  some  problems  no  conclusion  is  justifiable  and  in 
some  no  explanation  may  be  called  for. 

A  few  regulations  that  are  desirable  for  notebook  work  are: 

(1)  All  work,  with  the  possible  exception  of  drawings,  should  be  in  ink. 

(2)  It  is  desirable  to  start  a  new  problem  or  topic  on  a  new  page. 

(3)  A  margin,  at  least  on  the  left-hand  side  of  the  page,  should  be  ob- 
served. 

(4)  The  first  few  pages  may  be  left  blank  for  the  purpose  of  later  writing 
a  Table  of  Contents. 

(5).  Underlining  of  titles,  etc.,  is  desirable.  Too  much  underlining  is  un- 
desirable. 

Equipment.  In  almost  every  case  the  apparatus  is  so  simple  that  the 
work  may  be  carried  on  in  an  ordinary  classroom.  It  should  be  equipped, 
however,  with  gas,  water,  and  electricity  if  possible. 

Use  may  well  be  made  of  motion  pictures  and  lantern  demonstrations  in 
connection  with  many  of  the  subjects. 


SUGGESTIONS  TO  TEACHERS 


395 


APPARATUS  NEEDED  FOR  THE  COURSE 
The  following  material  is  needed  for  each  member  of  the  class: 


UNIT  I 

A  glass  tumbler 
Baking-dish 
Graph  paper 
Fountain  pen  filler 
Glass  plate 
Test  tubes 
Preserve  jar  with  cover  and 

rubber 
Glass  vial 
Scalpel 

UNIT  II 
Weather  maps  of  consecutive 

dates 
Blank  weather  maps 


UNIT  III 
Syracuse  watch  glass  or  butter  plate 

UNITY 

Scissors  —  may  be  brought  from  home 
Nutcracker  —  may  be  brought  from 

home 
Forceps    or    sugar    tongs  —  may    be 

brought  from  home 
Egg-beater  —  may  be  brought  from 

home 
Screw 
Magnet 

Nails  of  iron  and  steel 
Tacks 
Iron  filings 


The  following  material  is  needed  in  smaller  quantities,  enough  to  furnish 
apparatus  for  class  experiments: 


UNIT  I 
Balances,  platform  and  horn,  with 

weights  and  sand 
Glass  funnels 
Rubber  tissue 
Glass  tubing 
Barometer  tube 
Suction  pump 
Force  pump 
Exhaust  pump 
Aquarium  jar 
Rubber  tubing 
Model  of  ear 
Electric  bell 
Large  test  tube 
Rubber  stoppers  to  fit  large  test 

tubes  and  flasks 
Flasks 

Bunsen  burners 
Fire  extinguisher 
Physician's  thermometer. 
Atomizer 

Compound  microscope 
Glass  slides 
Bell  jar  with  opening  at  top 


Y-shaped  glass  tube 
Respiration  apparatus 

UNIT  II 
Distilling  apparatus  or  2  round  pans 

and  a  round  cake  tin 
3  lamp  chimneys 
Water  faucets 
Ether  can  with  metal  tubes 
Funnel  tube  with  stop-cocks 
Beakers 
Small  stewpans 
Chemical  thermometer 
Aluminum  kettle  cover 
Calorimeter 

Blackboard  wall  map  of  United  States 
Flower  pots  to  fit  tops  of  tumblers 
Graduate 
Lamp  wick 
Bottles 

UNI?  Ill 

Food  charts  (United  States  Depart- 
ment of  Agriculture) 
Asbestos  sheeting 


396 


SUGGESTIONS  TO  TEACHERS 


Cork  stoppers 

Ring  stand  with  rings  and  clamps 

Plates 

Sterilizer  (large  kettle  or  clothes 

boiler) 

Drying  racks 
Pail  with  false  bottom 

UNIT  IV 

Large  wooden  box 
Tin  tray 
Mirror 
Prism 

Reading-glass 
Kerosene  lamp 
Lava  tip  for  gas  burner 
Welsbach  mantle  burner 
Dry  batteries 

Wire,  German  silver  and  copper, 
various  sizes 


Incandescent  bulbs 
Copper  and  zinc  strips 
Compass 
Switch 

Charts,  showing  temperature  January 
and  July 

UNITY 

Meter  stick  painted  black  and  white 

Pulleys 

Board  4  feet  long 

Toy  car 

Telegraph  instruments 

Cup  and  saucer 

Wooden  blocks 

Iron  block 

Working  model  of  steam  engine 

Coffee  pot 

Electric  motor. 

Galvanometer 


MATERIALS  NEEDED 


UNIT  I 


Mercury 

Candles 

Potassium  chlorate 

Manganese  dioxide 

Calcium  carbonate 

Hydrochloric  acid 

Sodium  nitrate 

Marble  chips 

Lime  water 

Phosphorus 

Sulphur 

Seeds,  kidney  beans,  peas,  radish, 

corn,  etc. 
Iodine 
Joss  sticks 
Agar 

Methylene  blue 
Salt 

Hydrogen  peroxide 
Mercuric  chloride 
Carbolic  acid 


UNIT  II 


Carmine 
Litmus  paper 


UNIT  III 
Nitric  acid 

Ammonium  hydroxide 
Fehling's  solution 
Alcohol 
Sealing  wax 
Cotton  flannel 
Cheesecloth 

UNIT  IV 
Portland  cement 
Sand 
Pebbles 

Plaster  of  Paris 
Wood  sections 
Bricks 

Granite  pieces 
Sandstone  pieces 
Limestone  pieces 
Marble  pieces 
Cardboard 
Sulphuric  acid 
Soft  coal 

Cotton  bolls  and  fiber 
Raw  wool 
Silk  cocoons 


SUGGESTIONS  TO  TEACHERS  397 

Oil  Sal  soda 

Chloride  of  lime  Oxalic  acid 

The  following  materials  should  be  procured  as  needed: 

UNIT  I  Molasses 

Onion  Flour 

Fern  Yeast  cakes 

Beef  broth  Tomatoes 

UNIT  III  UNIT  IV 

Eggs  Lemon 

Sugar  Vinegar 

Cornstarch 

Lard  UNIT  V 

Celery  Flowers 

Bread  Apples 

Milk  Bean  or  pea  pods 

Potatoes 

PROJECT  PLANS 
PROJECT  I. 

Problems  I,  5,  6,  7,  and  1 1  should  be  done  by  each  pupil  in  the  classroom 
(pupils'  problems). 

Problems  2,  3,  4,  8,  9,  10,  and  12  are  class  problems.  One  or  more  pupils 
or  the  teacher  may  act  as  agents  of  the  class  in  actually  performing  the 
experiment. 

Ask  boys  to  bring  a  football  to  use  in  problem  2  and  a  bicycle  pump  for 
problem  9. 

Before  beginning  problem  5,  it  is  well  to  make  arrangements  with  the 
nearest  local  weather  bureau  to  receive  regularly  copies  of  the  daily 
weather  map.  These  should  be  posted  daily  in  the  room.  They  are  studied 
in  more  detail  in  Project  VI. 

Before  taking  problem  10  some  pupil  or  a  group  should  have  made  the 
school  aquarium. 

PROJECT  II. 

Problems  4,  5,  6 pupils'. 

Problems  i,  2,  3,  7,  8,  9,  10,  n class. 

Encourage  the  pupils  to  try  as  many  experiments  as  possible  at  home, 
after  trying  them  in  school. 

PROJECT  III. 

Problems  I,  4,  10,  13 pupils'. 

Problems  2,  3,  5,  6,  7,  12,  14 class. 

Problems  8  and  9.  The  slides  should  be  prepared  by  the  teacher,  but 
each  pupil  should  have  the  opportunity  of  examining  the  cells, 


398  SUGGESTIONS  TO  TEACHERS 

The  seeds  for  problems  6  and  7  should  be  soaked  overnight  and  started 
to  germinate  at  least  four  days  before  the  problems  are  to  be  taken. 

The  respiration  apparatus  needed  for  problem  13  may  be  in  the  physi- 
cal training  department  of  the  school. 

PROJECT  IV. 

Problem  I  should  be  assigned  for  home  work. 

Problems  2,  3,  5,  6 class. 

Problems  4,  7 pupils'. 

Nutrient  agar  may  be  obtained  from  the  local  board  of  health  or  pre- 
pared in  the  following  way.  Have  it  ready  several  days  before  it  is  needed 
for  problems  3  and  5. 

Measure  1000  c.c.  water,  10  g.  salt,  10  g.  peptone,  10  g.  Liebig's  beef 
extract,  and  10  g.  agar-agar. 

Dissolve  the  beef  extract  in  the  water.  Add  agar  cut  into  small  pieces, 
salt,  and  peptone.  Heat  until  the  agar  dissolves.  Add  cooking  soda  until 
the  solution  is  alkaline,  as  tested  by  litmus  paper. 

Have  ready  an  Erlenmeyer  flask  and  a  glass  funnel  tube  which  have  been 
sterilized  by  boiling  in  water.  Place  absorbent  cotton  in  the  funnel,  and 
filter  the  liquid  while  hot.  Plug  the  mouth  of  the  flask  with  absorbent 
cotton. 

Sterilize  for  half  an  hour.  The  best  way  is  to  use  a  steam  sterilizer,  but 
fair  results  may  be  obtained  by  setting  the  flask  in  a  pail  or  double  boiler 
partly  filled  with  water  and  tightly  covered. 

Pour  the  hot  solution  into  Petri  dishes  which  have  been  sterilized,  or 
into  sterilized  test-tubes.  Allow  them  to  cool,  keeping  the  agar  covered 
and  in  a  place  free  from  dust. 

PROJECT  V. 

If  it  is  inconvenient  to  take  the  whole  class  to  the  waterworks  (problem 
l),  assign  the  trip  as  an  individual  or  group  project. 

Problems  2,  3  5,  8,  9,  II,  12,  13 class. 

Problems  4,  7,  10,  14 home. 

Problem  6 pupils'. 

The  apparatus  for  problem  9  must  be  made  in  advance.  If  you  have  no 
soldering  apparatus,  a  tinsmith  will  solder  the  tubes  for  a  few  cents. 

Buy  the  eggs,  meat,  and  potatoes  for  problems  n,  12,  and  13  the  day 
they  are  needed. 

PROJECT  VI. 

Problems  I,  2,  9,  10,  12,  13 pupils'. 

Problems  3,  4,  5,  6,  7,  8,  n class. 

Arrangements  should  be  made  with  the  nearest  weather  bureau  to  have 
a  weather  map  sent  each  day. 


SUGGESTIONS  TO  TEACHERS  399 

PROJECT  VII. 

Problem  I  may  be  a  class  trip,  or  assigned  as  preparation,  with  discus- 
sion afterwards. 

Problems  2,  6,  9 pupils'. 

Problems  3,  4,  5,  7 class. 

Problem   8 home. 

PROJECT  VIII. 

Problems  i,  2,  9,  12,  14 pupils'. 

Problems  3,  4,  5,  6,  7,  8,  —  the  first  part  may  be  performed  by  the  teacher 
or  by  a  committee,  but  the  second  part  should  be  performed  by  the  in- 
dividual pupils. 

Problems  10,  n,  13 class. 

Problems  15,  16,  17 home. 

PROJECT  IX. 

Problems  i,  3,  4,  6,  7 home. 

Problem  2 class. 

Problems  5,8 pupils'. 

PROJECT  X. 

Problems  i,  3,  4,  5,  13 home. 

Problems  2,  6,  n,  12 class. 

Problems  7  and  14  may  be  class  trips  or  group  projects. 

Problems  8,  9,  10,  especially  for  girls,  may  be  done  in  school  or  at  home. 

Great  care  must  be  used  in  working  with  bacteria  to  prevent  any  infection. 

PROJECT  XL 

Problems  i,  2,  12 home. 

Problems  2,  3,  7 group  or  individual  projects. 

Problems  5,  8,  9,  10,  u,  14 pupils'. 

Problems  6,  13 class. 

The  best  material  for  problem  10  is  Hough's  Wood  Sections  which  are 
sold  by  Romeyn  B.  Hough,  Lowville,  N.  Y. 

PROJECT  XII. 

Problems  1,7 home. 

Problems  2,  4,  5,  6,  9,  n,  12,  13,  14, 15,  16. .  .class  or  pupils'. 

Problems  3,  10 pupils'. 

Problem  8 individual  project. 

PROJECT  XIII. 

Problems  i,  3,  5,  8,  9 class. 

Problems  2,  4,  5,  6,  7,  1 1 home. 

Problem  10 pupils'. 


400  SUGGESTIONS  TO  TEACHERS 

PROJECT  XIV. 

Problems  I,  5,  6,  7,  8 pupils'. 

Problems  2,  9,  n,  12,  13 home. 

Problems  3,  4,  10 class. 

Problems  14,  —  part  I  at  school,  parts  2\  3,  and  4  at  home. 

PROJECT  XV. 

Problems  I,  2,  4  5,  9,  10,  15 class. 

Problems  3,  13,  14 home. 

Problems  6,  7,  8,  n,  12 pupils'. 

PROJECT  XVI. 

Problems  1,2,3,4 pupils'. 

Problems  5,  6,  7,  8,  9 class. 

Problems  10,  n  may  be  class  trips  or  individual  projects. 

PROJECT  XVII. 

Problems  i,  2,  3,  4,  5,  6,  7 class. 

Problem  8  may  be  a  class  trip  or  individual  project. 

PROJECT  XVIII. 

Problems  1,3 :  .  pupils'. 

Problem  2 class. 

Problems  4,  5,  may  be  class  trips  or  group  projects. 
Problem  6 .  .  . .  home. 


LESSON  PLANS  FOR  A  ONE- YEAR  COURSE  IN 
GENERAL  SCIENCE 

(Five  times  a  week  in  the  9th  year.     This  plan  has  been  successfully 
followed  in  a  large  boys'  high  school) 

UNIT  I.  THE  AIR  AND  HOW  WE  USE  IT 
PROJECT  I.  THE  AIR  A  REAL  SUBSTANCE 

Lesson  Topics  and  Problems 

No. 

1 .  Scope  and  aim  of  General  Science  —  Life's  necessities  —  Evidence 
;  that  air  is  real 

Problem  —  What  is  in  an  empty  glass? 

2.  Air  has  weight. 

Problem  —  Does  the  air  weigh  anything? 

3.  The  atmosphere  an  ocean  of  air. 
Problem  —  Does  the  air  exert  a  pressure? 


SUGGESTIONS  TO  TEACHERS  401 

Lesson  Topics  and  Problems 

No. 

4.  Measuring  atmospheric  pressure  —  Galileo  and  Torricelli. 
Problem  —  How  can  air  pressure  be  measured? 

5.  Forecasting  weather  by  means  of  the  barometer. 

Problem  —  What  is  the  relation  between  air  pressure  and  the 
weather? 

6.  Air  pressure  and  the  suction  pump. 
Problem  —  Why  does  water  rise  in  a  pump? 

7.  The  force  pump  and  the  exhaust  pump. 

8.  The  bicycle  pump. 

Problem  —  How  does  a  bicycle  pump  work? 

9.  Air  pressure  and  the  action  of  the  siphon  —  Uses  of  the  siphon. 
Problem  —  To  take  the  water  out  of  a  vessel  by  using  a  siphon. 

10.  Air  pressure  and  the  human  body  —  Structure  of  the  ear  —  Na- 
ture of  sound  —  Air  transmits  sound. 

II  and  12.  Summary  and  review.  (Individual  projects  not  previously 
taken  up.) 

PROJECT  II.  AIR  AND  FIRE 

1.  Uses  of  fire  —  A  fire  needs  air  —  Some  of  the  characteristics  of 
oxygen,  nitrogen,  and  carbon  dioxide. 

Problem  —  Is  an  air  supply  necessary  for  burning? 

Problem  —  Which  of  the  gases  in  the  air  helps  to  make  things  burn? 

2.  Composition  of  the  air  —  Lime  water  test  for  carbon  dioxide  — 
Extinguishing  fires. 

Problem  —  A  test  for  carbon  dioxide. 

Problem  —  Does  the  air  contain  carbon  dioxide? 

3.  Products   of   burning,    water   vapor   and   carbon   dioxide;   their 
origin. 

Problem  —  What  substances  are  produced  when  a  candle  burns? 
Problem  —  What  substances  are  produced  when  a  piece  of  wood 
burns? 

4.  Elements  and  compounds  —  Conditions  necessary  for  oxidation 
and  results  of  oxidation  —  Kinds  of  oxidation  with  examples. 
Problem  —  What  proportion  of  the  air  consists  of  oxygen? 

5.  Study     of     oxidation     continued  —  Chemical     changes  —  Inde- 
structibility of  matter  —  Transformation  of  matter  —  Illustrations. 

6.  Study  of  the  kindling  temperature  —  Matches,  how  made  and 

the  principles  underlying  their  use. 
Problem  —  What  is  the  relation  between  temperature  and  burning? 

7.  Preventing  and  extinguishing  fires  —  A  common  fire  extinguisher. 
Problem  —  To  make  and  use  a  model  of  a  fire  extinguisher. 

8.  Review. 


402  SUGGESTIONS  TO  TEACHERS 

PROJECT  III.  AIR  AND  BREATHING 

Lesson  Topics  and  Problems 

No. 

1 .  Breathing,  a  life  activity  —  Rate  of  breathing  in  relation  to  amount 
of  activity  —  Comparison  with  a  steam  engine  —  Heat  produc- 
tion in  relation  to  rate  of  breathing. 

Problem  —  How  does  exercise  affect  the  rate  of  breathing? 
Problem  —  What  is  the  body  temperature? 

2.  Air  that  we  breathe  in  compared  with  air  that  is  exhaled  —  How 
breathing  changes  the  composition  of  the  air. 

Problem  —  Is  carbon  dioxide  given  off  in  breathing? 
Problem  —  Is  water  vapor  given  off  in  breathing? 

3.  How  the  composition  of  the  air  is  changed  by  the  breathing  of 
other  animals  besides  man  and  of  plants. 

Problem  —  Does  a  fish  give  off  carbon  dioxide?  (Fish  and  lime 

water.) 

Problem  —  Do  germinating  seeds  give  off  carbon  dioxide? 

Problem  —  Do  germinating  seeds  use  oxygen? 

4.  The  human  body,  a  machine  —  The  units  of  structure,  cells  — 
Breathing  occurs  in  cells  —  Parts  of  cells  —  Tissues  and  organs. 
Problem  —  Cells  from  the  inside  lining  of  the  mouth  seen  under 
the  microscope. 

5.  The  cells  of  the  blood,  especially  the  work  of  the  red  corpuscles. 
Problem  —  Red  corpuscles  under  the  microscope. 

6.  The  human   breathing  organs  —  Where   the  oxygen   enters   the 
blood  and  where  the  carbon  dioxide  leaves  it. 

7.  Breathing  motions  and  how  caused. 

Problem  —  How  does  a  person  breathe?  (bell  jar  exp.) 

8.  Value  of  deep  breathing  —  Oxidation  in  the  cells  and  the  produc- 
tion of  wastes. 

Problem  —  What  is  my  chest  expansion? 

9.  Principles  of  first-aid,  artificial  respiration. 
Problem  —  Demonstrate  artificial  respiration. 

10.      Review. 

PROJECT  IV.  AIR  AND  HEALTH 

1.  Importance  of  fresh  air  —  Factors  controlling  ventilation  —  Tem- 
perature, air  in  motion,  moisture,  possible  presence  of  foreign  ma- 
terials, composition  of  air. 

2.  Methods  of  cleaning  and  dusting  —  Review  ventilation. 
Problem  —  What  is  the  best  way  to  ventilate  my  living-room? 
(Use  joss  sticks  to  show  whether  air  is  in  motion.) 

Problem  —  What  is  the  best  way  to  ventilate  the  schoolroom? 


SUGGESTIONS  TO  TEACHERS     .         403 

Lesson  Topics  and  Problems 

No. 

3.  Air  and  disease  —  Enemies  of  health  —  Bacteria,  their  forms  and 
characteristics. 

Problem  —  Does  the  air  contain  any  bacteria? 

4.  How  bacteria  enter  the  body  —  Methods  of  attacking  the  body 
—  A  study  of  consumption. 

Problem  —  What  is  the  effect  of  sunlight  on  bacteria? 

5.  Diphtheria  and  the  antitoxin  treatment. 

6.  Defenses  of  the  body  against  bacteria;  external  and  internal  de- 
fenses. 

7.  Carriers  of  disease  —  How  colds  are  spread  —  Importance  of  keep- 
ing in  good  condition  and  how  this  may  be  done. 

8.  Effects  of  alcohol  and  tobacco  —  Seasons  in  relation  to  the  prev- 
alence of  some  diseases. 

Problem  —  Graphs  to  illustrate  the  prevalence  of  consumption, 
pneumonia,  and  diphtheria  at  different  seasons.  (Graphs  made 
from  statistics  showing  the  deaths  by  months  in  New  York  State.) 

9.  How  to  care  for  the  sick  —  Antiseptics  and  germicides  —  What 
communities  can  do. 

Problem  —  To  show  the  action  of  some  antiseptics  and  germicides. 
10.      Review. 

UNIT  II.  WATER  AND  HOW  WE  USE  IT 
PROJECT  V.  WATER  IN  OUR  HOUSES 

1.  Water  a  necessity  of  life  —  The  human  body   needs  water  — 
Sources  of  drinking-water  —  Pure  and  impure  water. 

Problem  —  A  trip  to  a  reservoir  or  pumping-station. 

2.  Kinds  of  impurities  in  water  —  Typhoid  fever  a  disease  often 
spread  by  impure  water. 

Problem  —  Comparison  of  relative  purity  of  tap  water  with  boiled 

water. 

Problem  —  To  purify  water  by  distillation. 

3.  Continue  study  of  typhoid  fever  and  discuss  problems  2  and  3. 

4.  Water  pressure  and  water-supply  systems. 
Problem  —  How  does  water  rise  in  pipes? 
Problem  —  How  does  a  water  faucet  work? 

5.  A  house  piping  system  —  A  hot-water  heater  —  Water  pipes  of 
a  house. 

Problem  —  To  trace  cold-water  piping  system  of  my  house. 
Problem  —  How  is  my  house  supplied  with  hot  water? 
Problem  —  To  trace  hot-water  piping  system. 

6.  Review  piping  systems  —  Sewage  disposal. 


404  SUGGESTIONS  TO  TEACHERS 

Lesson  Topics  and  Problems 

No. 

7.  Water  changes  from  one  form  to  another  —  Water  freezes  to  ice  — 
Water  changes  to  water  vapor  —  Steam  —  Review  of  physical  and 
chemical  changes. 

Problem  —  How  is  water  affected  by  heating? 
Problem  —  How  is  water  in  hot- water  tank  heated? 

8.  Cooking  foods  by  boiling  —  Changes  produced  in  food  by  boiling. 
Problem  —  Cooking  an  egg. 

9.  Water  as  a  solvent  —  Hard  and  soft  water. 
Problem  —  Is  the  water  in  my  home  hard  or  soft? 

10.      Review. 

PROJECT  VI.  WATER  IN  THE  AIR 

1.  The  weather  and  the  work  of  the  Weather  Bureau. 
Problem  —  To  keep  a  weather  record. 

2.  Water  in  an  invisible  form  in  the  air  —  How  water  vapor  gets  into 
the  air  —  Where  it  comes  from  —  Evaporation  from  plants. 
Problem  —  How  does  water  vapor  get  into  the  air? 

3.  Temperature  and  the  thermometer,  Centigrade  and  Fahrenheit. 
How  is  water  affected  by  changes  in  temperature? 

Problem  —  How  is  temperature  measured? 

4.  The  Wind  —  Winds  of  the  world. 
Problem  • —  What  makes  the  wind? 

5.  Temperature  and  the  amount  of  water  vapor  in  the  air. 
Problem  —  What  makes  the  rain? 

Problem  —  What  makes  the  dew? 

6.  Humidity  of  the  air  —  Condensation  —  Dew  and  its  formation 
—  Kinds  of  clouds  —  Thunderstorms. 

Problem  —  To  understand  a  weather  map. 
Problem  — To  keep  a  graph  of  the  weather. 

7.  Foretelling  a  storm  —  Review. 

8.  Path  of  storms  —  The  value  of  rain. 
Problem  —  To  trace  the  course  of  a  storm. 
Problem  —  What  paths  do  storms  follow? 

9.  Problem  —  A  trip  to  the  local  weather  bureau. 
10.      Review. 

PROJECT  VII.  WATER  AND  THE  SOIL 

1 .  How  soil  is  made  —  Value  of  water  in  the  soil  —  What  soil  con- 
tains. 

Problem  —  What  does  soil  contain? 

2.  Kinds  of  rocks;  igneous,  sedimentary,  metamorphic. 


SUGGESTIONS  TO  TEACHERS  405 

Lesson  Topics  and  Problems 

No. 

3.  Action  of  water  in  making  soil  —  Action  of  ice  —  of  wind  —  of 
air  —  of  plants  —  of  animals. 

4.  Problem  —  A  field  trip  to  study  formation  of  soil. 

5.  Plants  need  water  —  Water  in  the  soil  —  How  water  rises  in  the 
soil  —  How  to  save  moisture  in  the  soil. 

Problem  —  How  does  water  rise  in  the  soil? 
Problem  —  What  is  the  value  of  a  fine  surface  layer? 

6.  Review  —  Variation   in  amount  of   rainfall   in   United   States  — 
Reclaiming  desert  regions  —  Reclaiming  swampy  regions. 

7.  Review. 

UNIT  III.  FOODS  AND  HOW  WE  USE  THEM 
PROJECT  VIII.  PLANTS  —  FOOD-MAKERS  FOR  THE  WORLD 

1 .  Foods,  a  necessity  of  life  —  Origin  of  foods  —  Organic  and  inor- 
ganic foods. 

Problem  —  What  are  the  sources  of  our  food? 

2.  The  nutrients  —  Nutrients  can  be  shown  to  be  present  in  foods  by 
tests. 

Problem  —  Of  what  do  foods  consist? 
Problem  —  To  test  for  starch. 
Problem  —  To  test  for  grape  sugar. 

3.  Where  do  plants  get  their  foods?  —  Materials  plants  take  from  the 
soil. 

Problem  —  What  are  the  uses  of  each  part  of  a  plant? 

4.  Different  organs  of  a  plant  —  Root-hairs  —  How  a  root-hair  ab- 
sorbs water  —  Where  water  passes  through  the  plant. 

Problem  —  To  make  an  artificial  root-hair. 

5.  Where  foods  are  manufactured  —  Raw  materials  needed  —  Starch 
made  only  in  the  green  parts  of  a  plant. 

Problem  —  To  demonstrate  that  a  leaf  makes  starch. 

6.  Light  needed  in  starch-making  —  The  waste  product  —  Leaves 
make  all  the  organic  nutrients. 

7.  Helping  plants  make  foods;  fertilizers  —  Nitrogen-fixing  bacteria 
and  the  bacteria  of  decay  —  Taking  nitrogen  out  of  the  air  by  elec- 
tricity. 

8.  Review. 

PROJECT  IX.  FOODS  AND  THE  HUMAN  BODY 

I.      The  two  great  uses  of  foods  —  How  to  select  foods;  a  mixed  diet 
usually  desirable,  taste  and  digestibility,  quality  and  cleanliness. 
Problem  —  To  compare  some  common  foods  with  reference  to 
their  ability  to  build  up  the  body  and  furnish  energy. 


4o6  SUGGESTIONS  TO  TEACHERS 

Lesson  Topics  and  Problems 

No. 

2.  Meaning  of  "Calorie"  —  100  calorie  portions  —  Different  needs 
of  different  classes  of  people. 

Problem  —  How  is  heat  measured?   x 

3.  The  cost  of  foods. 

Problem  —  To  determine  the  relative  cost  of  some  common  foods. 

4.  The  human  food  tube  —  Digestion  and  its  use  —  Indigestion  — 
Its  common  causes  and  results  —  Means  of  prevention. 
Problem  —  What  are  the  parts  of  the  human  alimentary  canal? 

5.  Mouth  digestion  —  The  part  taken  by  the  teeth  —  Importance 
of  caring  for  the  teeth. 

Problem  — What  are  the  parts  of  a  tooth? 

6.  Where  the  food  becomes  part  of  the  blood  —  The  blood,  the  medium 
for  carrying  nourishment  to  all  parts  of  the  body  and  of  taking 
away  wastes  from  the  cells. 

7.  Where  the  wastes  leave  the  body  —  Importance  of  the  work  of  the 
lungs,  kidneys,  and  skin  —  Hygiene. 

8.  How  the  blood  is  made  to  circulate  —  The  heart  a  pump. 
Problem  —  To  determine  the  effect  of  exercise  upon  the  rate  of  the 
heart-beat. 

9.  Kind  and  general  work  of  different  blood  vessels — Treatment  for 
cuts. 

10.      Effects  of  alcohol  and  tobacco  upon  the  digestive  and  circulatory 
systems  —  Review. 

PROJECT  X.  FOODS  IN  THE  HOME 

1 .  Clean  foods  —  Why  foods  spoil  —  General  comparison  of  bacteria 
—  Molds  and  yeasts. 

2.  General  conditions  necessary  for  the  growth  of  these  micro-or- 
ganisms —  Action  of  bacteria  upon  foods  —  Ptomaine  poisoning. 
Problem  —  How  do  bacteria  get  upon  food? 

3.  Pasteurizing  milk  —  Importance  of  pure  milk. 
Problem  —  A  trip  to  a  large  milk  depot. 

4.  Action  of  molds  on  food  —  Conditions  necessary  for  mold  growth. 
Problem  —  Why  does  bread  mold? 

5.  Action  of  yeasts  on  foods  —  Yeasts  as  foes  and  as  friends. 
Problem  —  W7hy  does  yeast  cause  bread  to  rise? 

6.  Problem  —  A  trip  to  a  large  bakery. 

7.  How  to  protect  foods  against  yeasts,  molds,  and  bacteria  —  Dan- 
gers  in   meat  —  Cleanliness   in   the   kitchen  —  Work  of  a  city 
health  department. 

8.  A  trip  to  the  city  health  department. 
9  and  10.     Review. 


SUGGESTIONS  TO  TEACHERS  407 

INTRODUCTION  TO  THE  WORK  OF  THE  SECOND  TERM 

THE  FORCES  OF  NATURE 

Lesson  Topics  and  Problems 

No. 

1.  The  law  of  cause  and  effect  —  Matter  and  energy,  their  forms. 

2.  Examples  of  the  transformation  and  indestructibility  of  matter 
and  energy. 

3.  Source  of  all  energy  upon  the  earth  —  Kinetic  and  potential  en- 
ergy —  Conservation  of  certain  natural  resources  of  energy. 

4.  The  cause  of  the  seasons,  day  and  night,  the  stars,  the  sun,  and  the 
planets  —  Gravitation  and  Sir  Isaac  Newton. 


UNIT  IV.  PROTECTION  — HOMES  AND  CLOTHING 
PROJECT  XI.  BUILDING  OUR  HOMES 

1 .  Choosing  a  home  —  A  convenient  home  —  A  safe  home. 
Problem  —  To  examine  my  home  conditions. 

2.  How  a  house  is  built  —  The  foundation  — The  wall  —  The  floors 
—  The  roof. 

Problem  —  To  observe  a  house  while  it  is  being  built. 

3.  What  our  houses  are  made  of:  (i)  woods,  hard  and  soft  —  General 
uses  of  different  kinds. 

Problem  —  To  determine  the  uses  of  some  of  the  more  common 
kinds  of  wood. 

4.  What  our  houses  are  made  of:  (2)  bricks  —  Kinds  of  brick,  how 
made. 

Problem  —  Why  do  bricks  crumble? 

5.  What  our  houses  are  made  of:  (3)  concrete,  and  (4)  stucco  — How 
made. 

6.  What  our  houses  are  made  of:  (5)  building  stones  —  Granite,  sand- 
stone, limestone,  marble. 

Problem  —  To  compare  building  stones. 
7  and  8.  Review. 

PROJECT  XII.  LIGHTING  OUR  HOMES 

1.  A  well-lighted  house  —  How  our  houses  are  lighted  by  the  sun. 
Problem  —  How  do  we  get  sunlight? 

2.  Reflected  light  —  Reflection  from  mirrors. 
Problem  —  How  is  light  reflected? 

Problem  —  Where  does  a  reflected  image  appear  to  be? 

3.  Meaning  of  diffused  light. 

Problem  —  How  is  a  room  lighted  by  diffused  light? 


408  SUGGESTIONS  TO  TEACHERS 

Lesson  Topics  and  Problems 

No. 

4.  Meaning  of  refraction. 

Problem  —  What  is  the  principle  of  refraction? 

5.  The  colors  in  sunlight  —  Why  anything  has  color. 
Problem  —  What  are  the  colors  in  sunlight? 

6.  Lenses  —  Meaning  of  term  "focus." 
Problem  —  To  focus  the  sun's  rays. 

7.  The  camera  —  Its  essential  parts. 
Problem  —  To  make  a  pinhole  camera. 

8.  The  human  eye  —  Comparison  with  a  camera. 

9.  The  intensity  of  light. 

Problem  —  What  is  the  relation  between  the  amount  of  light  and 
the  distance  from  the  source? 

10.  Natural  and  artificial  light  —  Candle-light. 
Problem  —  How  does  a  candle  burn  and  give  light? 

11.  A  kerosene  lamp. 

Problem  —  How  does  a  kerosene  lamp  give  light? 

12.  Gas-lighting. 

Problem  —  How  does  a  mantle  increase  the  light  given  by  a  gas 
flame? 

13.  Electric  light. 

Problem  —  What  causes  an  incandescent  electric  lamp  to  give 
light? 

14.  Electric  cells  and  batteries. 
To  make  a  simple  electric  cell. 

15.  Conductors  and  insulation  —  Switches  —  Fuses  —  An  incandes- 
cent lamp. 

Problem  —  To  see  how  a  dry  cell  works  and  study  its  parts. 
Problem  —  To  connect  cells  to  form  a  battery. 

1 6.  Review. 

PROJECT  XIII.  HEATING  OUR  HOMES 

1.  Necessity  of  heat  —  Heat  from  the  sun  —  Kind  of  fuel. 

2.  Wood  as  fuel. 

Problem  —  What  are  the  parts  of  a  coal  range? 

3.  How  to  build  a  fire. 
Problem  —  To  build  a  fire. 

Problem  —  How  does  the  draught  of  a  stove  work? 

4.  The  best  temperature  for  houses  —  The  fireplace  as  a  heater. 
Problem  —  How  is  my  house  heated? 

5.  Three  ways  of  distributing  heat  —  Radiation  —  Conduction  — 
Connection. 

Problem  —  To  study  a  steam  boiler. 


SUGGESTIONS  TO  TEACHERS  409 

Lesson  Topics  and  Problems 

No. 

6.  The  stove  as  a  heater  —  A  jacketed  stove  —  A  hot-air  furnace. 

7.  Hot-water  heating  —  Steam  heat. 

8.  Gas  heaters. 

Problem  —  To  study  a  gas  stove. 
9  and  10.  Review. 

PROJECT  XIV.  CLOTHING  AND  ITS  CARE 

1.  Where  our  clothes  come  from  —  The  purpose  of  clothing. 

2.  An  envelope  of  air  about  our  bodies  —  Clothes  as  conductors  of 
heat. 

3.  Perspiration  —  The  cooling  effect  of  evaporation. 
Problem  —  Why  does  the  wind  chill? 

4.  Relation  between  color  of  clothing  and  their  warmth  —  Water- 
proof clothes. 

5.  Plant  fibers  —  Cotton,  flax,  and  other  plant  fibers. 

6.  Wool,  silk,  and  other  animal  resources  for  clothing. 

7.  Care  of  clothing,  water  the  universal  solvent  —  Action  of  soap  — 
Clothes  moths. 

Problem  —  Why  does  washing  with  soap  remove  dirt? 

8.  Review. 

PROJECT  XV.  WORK  WITH  EVERYDAY  MACHINES 

1.  Machines  in  our  homes  —  Work  requires  energy  —  Work  results 
in  motion. 

2.  Resistance  to  work  —  Weight  —  Friction  —  Inertia. 
Problem  —  What  are  the  causes  of  resistance  to  work? 
Problem  —  To  weigh  an  article. 

3.  How  work  is  measured. 

4.  Simple  machines  —  The  lever  —  Three  types. 
Problem  —  To  study  the  three  types  of  levers. 

5.  Meaning  of  the  term  "mechanical  advantage"    -The  efficiency 
of  a  machine. 

Problem  —  WThat  are  the  advantages  of  using  a  lever? 

6.  A  modified  lever  —  The  crank  and  axle. 

Problem  —  To  study  a  crank  and  axle  machine  —  The  egg-beater. 

7.  Another  modified  lever  —  The  pulley. 
Problem  —  How  do  pulleys  work? 

8.  The  inclined  plane  —  Its  mechanical  advantage. 

Problem  —  To  use  an  inclined  plane  and  find  the  advantage. 

9.  A  modified  inclined  plane  —  The  wedge. 
Problem  —  To  study  a  wedge  —  The  knife  blade. 


410  SUGGESTIONS  TO  TEACHERS 

Lesson  Topics  and  problems 

No. 

10.  The  screw  —  An  inclined  plane. 
Problem  —  To  study  a  screw. 

11.  Galileo,  a  great  inventor  —  The  invention  of  the  pendulum  clock. 
Problem  —  What  is  the  use  of  a  pendulum  in  a  clock? 

12.  Review. 

PROJECT  XVI.  COMMUNICATION 

1 .  Importance  of  communication  to  our  civilization — Organs  of  speech. 

2.  Electricity  and  modern  methods  of  communication. 
Problem  —  What  is  meant  by  magnetic  attraction? 

3.  Magnets  and  lines  of  force  —  Permanent  and  temporary  magnets. 
Problem  —  What  is  the  difference  between  a  temporary  and  a  per- 
manent magnet? 

4.  Like  poles  repel  —  Unlike  poles  attract. 

Problem  —  Which  magnetic  poles  attract  and  which  repel  each 

other? 

Problem  —  To  study  the  lines  of  force  about  a  magnet. 

5.  The  compass  and  its  uses  —  Lines  of  force  about  an  electric  wire. 
Problem  —  To  observe  whether  there  are  any  lines  of  force  about 
a  wire  carrying  an  electric  current. 

6.  An  electromagnet. 

Problem  —  To  make  an  electromagnet. 

7.  The  electric  bell. 

Problem  —  What  makes  an  electric  bell  ring? 

8.  The  telegraph  —  Submarine  cables  —  Wireless  telegraph. 
Problem  —  How  does  a  telegraph  instrument  work? 

9.  The  telephone  —  Wireless  telephone. 
Problem  —  How  does  the  telephone  work? 

10.  Problem  —  A  trip  to  a  telephone  exchange. 

11.  The  making  of  a  newspaper. 
Problem  —  A  trip  to  a  newspaper  office. 

12.  Review  and  individual  projects. 

PROJECT  XVII.  TRANSPORTATION 

1.  Importance  of  transportation  in  everyday  life  —  Animal  power 
compared  with  steam  and  electric  power. 

2.  Water  as  a  medium  for  transportation  —  Why  substances  float  or 
sink. 

Problem  —  Why  do  some  objects  float  in  water? 

3.  Archimedes'  principle  —  Specific  gravity  —  Submarines  and  the 
floating  of  iron  ships. 

Problem  —  To  find  the  specific  gravity  of  iron. 


SUGGESTIONS  TO  TEACHERS  411 

Lesson  Topics  and  Problems 

No. 

4.  Steam  engines  —  The  first  steam  engine  —  The  principle  of  the 
steam  engine  —  Locomotives  and  steamships. 

Problem  —  What  is  the  principle  of  the  steam  engine? 

5.  Steam  and  gas  engines  compared  —  How  a  gas  engine  works  — 
The  automobile. 

Problem  —  What  is  the  principle  of  a  gas  engine? 

6.  Electric  power  —  The  parts  and  working  of  an  electric  motor  — 
Electric  cars  and  locomotives. 

Problem  —  To  study  the  parts  of  an  electric  motor  and  see  how 
it  works. 

7.  The  dynamo  compared  with  an  electric  motor  —  The  principle  of 
the  dynamo. 

Problem  —  What  is  the  fundamental  principle  of  a  dynamo? 

8.  Power  stations. 

Problem  —  To  visit  an  electric  power  plant. 

9.  Kinds  of  water-wheels. 

10.  Water-power  and  the  protection  of  forests. 
II  and  12.  Review. 

PROJECT  XVIII.  LIFE  —  ITS  ORIGIN  AND  BETTERMENT 

1.  The  changing  life  upon  the  earth  —  All  life  conies  from  life  — 
Methods  of  reproduction. 

2.  Seeds  and  eggs  —  A  baby  plant  in  the  making  —  The  parts  of  a 
flower. 

Problem  —  What  are  the  parts  of  a  flower? 

3.  Pollen  grains  and  their  germination. 

Problem  —  To  grow  pollen  tubes  and  examine  them  under  the 
microscope. 

4.  How  a  part  of  the  pollen  grain  reaches  the  egg  cell  —  Pollination 
and  fertilization. 

5.  Development  of  the  fertilized  egg. 
Problem  —  How  does  a  fruit  develop? 

6.  Reproduction  in  higher  forms  of  animals. 

7.  The  meaning  of  heredity,  variation,  and  selection. 
Problem  —  A  field  trip  to  observe  the  struggle  for  existence. 

8.  Charles  Darwin  and  evolution. 

9.  Improving  living  conditions  —  Preventive  medicines  —  Destroy- 
ing flies  and  mosquitoes. 

10.       Improving  one's  environment. 

Problem  —  How  can  I  improve  my  environment? 
II  and  12.  Review. 


INDEX 


Air,    3-67;    brakes,    17;  chamber,  2; 

compressed,   17;  envelope  of,  294; 

in  soil,  137;  liquid,  17;  pressure,  4, 5. 
Airplane,  3,  19,  20,  349. 
Alcohol,  effects  of,  62,  186. 
Alimentary  canal,  166. 
Alluvium,  129. 
Anopheles,  388. 
Anther,  379. 
Anti-cyclone,  114. 
Antiseptics,  65,  66. 
Antitoxin,  60,  386. 
Aquarium,  2,  7,  8. 
Archimedes'  principle,  354. 
Armature,  343. 
Arteries,  183. 
Artesian  wells,  84. 
Automobile,  331,  349,  362-65. 

Bacteria,    disease-producing,    56-63 ; 

flies  carry,  202;   in  water,    79-81; 

keeping  off  foods,  199,  200;  of  decay, 

88,  132;  nitrogen-fixing,  160. 
Bacteriology,  386. 
Balance,  323;  equal  arm,  322;  spring, 

322. 

Ball  bearings,  320. 
Balloons,  3,  14,  18,  353. 
Barometer,  aneroid,  n;  mercurial,  6, 

10-12. 

Batteries,  266. 
Bicycle,  331. 
Biology,  377. 
Block  and  tackle,  328. 
Blood  vessels,  183. 
Boiling,  effect  upon  foods,  76,  77,  91, 

92 ;  point,  90. 
Bread-mixer,  327. 

Breathing,  34-49;  organs  of,  38,  39. 
Bricks,  233,  242. 
Bunsen  burner,  264. 
Buoyancy,  354. 

Cable  car,  367. 
Caisson,  20. 
Calorie,  165,  168. 
Camera,  260;  pinhole,  252. 
Candle,  253,  262. 

Canning,  cold-pack  method,  200;  ber- 
ries, 193;  vegetables,  192. 
Capillaries,  47. 
Capillary  action,  134. 


Capillary  tubes,  123. 

Carbohydrates,  153,  155. 

Carbon,  262. 

Carbon  dioxide,  given  off  in  breathing, 

35,  36;  in  air,  26,  27;  oxidation,  30; 

test  for,  23;  used  by  leaves,  150. 
Carburetor,  363. 
Cause  and  effect,  law  of,  208. 
Cells,  37,  42-44,  158,  377. 
Celluloid,  256.  ' 
Cellulose,  297. 
Cement,  243. 
Cesspool,  88. 

Chemical  changes,  153,  154. 
Chemistry,  28. 
Chest,  expansion  of,  40. 
Chlorophyll,  158. 
Circulation,  182,  186. 
Clay,  122. 

Cleanliness  of  foods,  189. 
Clock,  317,  330. 
Clothes,  moths,  305. 
Clothing,  286-306;  care  of,  300;  color 

of,  296;  conduction  of  heat,  294; 

purpose  of,  293;  science  of,  286,  287; 

waterproof,  296. 
Clotting  of  blood,  184. 
Clouds,  109. 

Coal,  127;  hard,  271,  275;  soft,  276. 
Coffee,  1 80. 
Cogwheel,  311. 
Coke,  272. 

Colors,  251,  258,  259. 
Combustion,  27. 
Communication,  333-48. 
Compass,  341. 
Compounds,  28,  29. 
Concrete,  229,  243. 
Condensation,  109. 
Conduction,  278,  281. 
Conductivity  of  woods,  241. 
Conductors,  267,  287. 
Constellations,  216. 
Consumption,  57-62. 
Convection,  87. 
Cooker,  fireless,  284. 
Corpuscles,  white,  59,  60. 
Cotton,  290,  296. 
Crank  and  axle,  326. 
Cravenetting  process,  296. 
Cross-pollination,  375,  382,  383;  arti- 

5dal,  383,  385. 


INDEX 


413 


Currents,  279. 

Cuts,  treatment  of,  183. 

Cyclone,  113. 

Dams,  137. 

Day,  220. 

Dentine,  185. 

Dew,  100,  no. 

Diaphragm,  45. 

Diesel  engine,  362. 

Diet,  1 68. 

Digestion,  181,  182,  186. 

Diphtheria,  60,  63,  65. 

Dishwashing,  204. 

Disinfection,  56. 

Division  of  labor,  197. 

Drainage,  226. 

Drugs,  1 80. 

Dust,  55. 

Dynamo,  351,  367,  368. 

Ear,  8,  14,  15. 

Earth,  217,  218. 

Earthworms,  132. 

Eclipses,  224. 

Efficiency,  322. 

Eggs,  377,  380. 

Egyptians,  338. 

Electric,  bell,  335,  339,  34°,  342;  cars, 
366,  367;  cells,  266;  locomotives, 
366,  367;  motor,  351,  366,  367; 
power,  365;  power  station,  366,  368. 

Electricity,  cooking  with,  284;  dry 
cell,  255,  256;  fuses,  267;  modern 
methods  of  communication,  339;  ni- 
trogen out  of  air,  161 ;  pressure,  265; 
resistance,  267;  simple  cell,  254,  255. 

Electro-magnet,  335,  340,  342,  366. 

Elements,  28,  29. 

Elevation  and  air  pressure,  14. 

Emulsion,  302. 

Enamel,  185. 

Energy,  209-16,  318;  conservation  of, 
215,  216;  forms  of,  213;  indestructi- 
bility of,  214;  kinetic,  212;  poten- 
tial, 212,  213;  sources,  214-16; 
transformed,  214. 

Engine,  gas,  351,  361,  362;  steam,  350, 
35.6-58,  36i. 

Environment,  376,  390. 

Enzymes,  182,  198. 

Equinox,  219. 

Erosion,  129. 

Eustachian  tube,  15. 

Evaporation,  90,  295. 

Evolution,  373,  384. 


Exercise,  34,  62,  167. 
Eye,  261. 


Fat,  I43,.i53,  155- 

Fertilization,  380. 

Fertilizers,  159-61. 

Filter,  81;  beds,  88. 

Fire,  21-33;  engine,  12;  fire-extin- 
guisher, 25-27;  protection,  227;  to 
build  a,  272,  276. 

Fireplace,  277. 

Fish,  breathing  of,  38. 

Flax,  297. 

Flies,  202,  375,  387. 

Floating  of  iron  ships,  355. 

Flower,  374,  378. 

Fog,  109. 

Foods,  141-207;  conservation,  142; 
drying,  193,  201;  effect  of  bacteria 
and  molds,  189,  190;  manufacture 
of,  151;  necessity  of,  141;  origin  of, 
152,  153;  selection  of,  167,  179;  uses, 
164;  varying  amounts  needed,  169. 

Food  charts,  171-78. 

Food  table,  170,  171. 

Food  tube,  180. 

Football,  4. 

Foot-pound,  321. 

Force,  318;  acting,  309-11,  323;  force 
arm,  309;  resisting,  309,  310. 

Forces  of  nature,  208-24. 

Forests,  370. 

Freezing  point,  89. 

Friction,  320. 

Fruit,  374. 

Fuel,  275. 

Fulcrum,  307,  310,  311,  323. 

Furnace,  hot  air,  280. 

Gardens,  141,  151,  161. 

Gas,  engine,  351,  361,  362;  illuminat- 
ing, 24, 263 ;  mantle,  254, 264;  meter, 
264;  natural,  275,  283;  stove,  274. 

Gastric  juice,  182. 

Germicides,  65,  66. 

Germs,  56. 

Glaciers,  130. 

Gluten,  191. 

Granite,  244. 

Gravitation,  221. 

Great  War,  80,  142. 

Hail,  109. 

Headaches,  184;  powders  for,  167. 
Heat,   absorption,  289;    form  of  en- 
ergy, 213;  hot  water,  28 1 ;  steam,  283. 


INDEX 


Heaters,  gas,  283;  hot-water,  86,  87; 
kerosene  water,  87. 

Hieroglyphics,  338. 

Homes,  225-85;  building,  225-47; 
heating,  271-85;  lighting,  248-69. 

House,  a  convenient,  234,  235;  build- 
ing materials,  239,  240;  floors,  238; 
foundations,  237,  238;  plans,  229; 
roof,  239;  safe,  235,  236;  walls,  238; 
well-lighted,  248. 

Humidifier,  285. 

Humidity,  108. 

Humus,  122. 

Hydrogen,  262. 

Hygiene,  42. 

Ice,  89,  130. 
Image,  257. 
Incandescence,  265. 
Inclined  plane,  313,  322,  328. 
Indigestion,  184. 
Inertia,  308,  321. 
Inoculation,  387. 
Insulators,  267. 
Intestines,  181. 
Iodine  test,  145. 
Irrigation,  136. 

Jute,  297. 
Kite,  20. 

Lamp,  electric,  254;  incandescent,  268, 
kerosene,  253,  263. 

Larva,  389. 

Larynx,  338. 

Laws,  pure  food  and  drug,  205. 

Lens,  259,  260. 

Lever,  309,  322-25;  advantages  of, 
310;  three  types,  310. 

Light,  absorption  of,  256;  angle  of  in- 
cidence, 257;  angle  of  reflection, 
257;  candle,  262;  diffused,  250,  257; 
electric,  268;  form  of  energy,  213; 
intensity  of,  252,  253,  262;  reflec- 
tion of,  249,  256;  refracted,  258; 
travels  in  straight  lines,  256. 

Lightning,  no. 

Limestone,  245. 

Lime  water,  23,  191. 

Lines  of  force,  334,  335,  340,  342. 

Linotype,  337,  347. 

Liquids,  8. 

Litmus,  124. 

Loam,  134. 

Locomotive,  349,  358,  359,  366,  367. 


Lodestone,  340,  341. 
Lungs,  39,  45,  59. 

Machines,  307-32;  efficiency  of,  326; 
crank  and  axle,  311,  326;  inclined 
plane,  328;  lever,  322-26;  pulley, 
327;  screw,  329;  wedge,  329. 

Magnet,  340;  permanent,  334,  341, 
366;  temporary,  334,  341. 

Magnetic  attraction,  333,  340;  poles, 
334,  340,  366. 

Magnetite,  340. 

Mail  tubes,  pneumatic,  20. 

Malaria,  389. 

Manganese  dioxide,  22. 

Marble,  245. 

Matches,  31. 

Matter,  209;  change  in  form,  33;  in- 
destructibility of,  32,  33. 

Meat,  cuts  of,  203. 

Mechanical  advantage,  313,  325. 

Medicine,  preventive,  386. 

Milk,  201,  202. 

Mist,  109. 

Molds,  196,  197,  199,  200. 

Monotype,  337,  347. 

Moons,  219. 

Mosquitoes,  375,  388. 

Motion,  319. 

Narcotics,  186. 

Negative,  260. 

Nerves,  185. 

Neutralization,  293,  302,  304. 

Newcomen,  356. 

Night,  220. 

Nitrates,  160. 

Nitrogen,  23,  26. 

North  Pole,  217. 

Nutrients,  143,  153,  159. 

Offspring  and  parent,  383. 

Organs,  44;  of  breathing,  45;  of  diges- 
tion, 180-82;  of  a  plant,  154,  155; 
of  reproduction,  1 54, 377-83 ;  speech, 
16,  338- 

Osmosis,  156. 

Oxidation,  30,  31;  in  the  body,  46. 

Oxygen,  given  off  by  green  plants,  159; 
in  air,  24,  26,  27;  test  for,  22;  used 
in  breathing,  36,  41. 

Pancreatic  juice,  182. 
Parent  and  offspring,  383. 
Petals,  379. 
Phonograph,  331. 


INDEX 


415 


Phosphorus,  25. 

Photography,  260. 

Physical,  states,  89;  change,  153. 

Physics,  221. 

Piping  system,  house,  75,  76;  waste, 
86,  87. 

Plants,  141-63,  218-20,  223;  breath- 
ing, 38;  organs  of,  154,  155;  passage 
of  water  through,  156;  soil  in  rela- 
tion to,  132;  transpiration  of,  106; 
uses  of,  149;  water  need  of,  133. 

Platinum  wire,  268. 

Pneumonia,  59,  61,  63. 

Poles,  electric,  265. 

Pollen,  379;  grains,  379-81 ;  tubes,  374, 
38o. 

Potassium  chlorate,  22. 

Power,  electric,  365;  steam,  352,  359. 

Preservatives,  200. 

Pressure,  air,  4,  5,  9-14;  electrical,  265; 
gauge,  282;  root,  157;  water,  82. 

Printing  press,  333,  347. 

Propeller,  19. 

Protein,  143,  155- 

Protoplasm,  43,  290. 

Ptomaines,  197. 

Ptyalin,  182. 

Puddingstone,  127. 

Pulley,  312,  326,  327. 

Pulmotor,  48. 

Pump,  bicycle,  7, 13;  exhaust,  7,  12,16; 
force,  6,  7,  12;  suction,  6,  10,  12. 

Pumping  station,  20. 

Pupa,  299. 

Quarantine,  56. 
Quartzite,  127. 

Radiation,  277,  281. 
Railroads,  333,  361. 
Rain,  100;  value  of,  117;  amount  of 

rainfall,  136. 
Ramie,  298. 
Reflection,  250. 
Refraction,  250. 

Refrigerator,  195,  196;  iceless,  93. 
Reproduction,  377-83. 
Reservoirs,  70,  82. 
Resistance,  arm,  309,  311,  323;  causes 

of,  308. 

Respiration,  artificial,  40,  47. 
Rocks,  1 25 -2 7 ;igneous,  I25;metamor- 

phic,  127;  sedimentary,  126. 
Roots,    149;  canals,   185;  hairs,   155, 

156;  pressure,  157. 
Routes,  land,  361 ;  water,  360. 


Safety  valve,  282. 

Sailing  vessels,  3. 

Saliva,  166. 

Sand,  121,  122. 

Sandstone,  127,  245. 

Sanitation,  227. 

Screw,  315,  329. 

Seasons,  63,  219;  in  relation  to  disease, 

53,  54- 

Secretion,  181. 

Seeds,  145747,  377,  3&>. 

Selection,  385;  artificial,  386. 

Sepals,  379. 

Septic  tank,  88. 

Sewage,  88. 

Sewing  machine,  315,  316. 

Shale,  127. 

Ships,  floating  of  iron,  355. 

Signaling,  339. 

Silk,  291,  298;  artificial,  306. 

Silkworm,  299. 

Siphon,  7,  13. 

Skin,  295. 

Slate,  127. 

Smallpox,  386,  387. 

Soap,  292,  301. 

Soil,  1 19-40;  acid,  124,  138;  air  in,  137; 
alluvium,  129;  clay,  122;  humus, 
122;  kinds  of,  131;  making  of,  127- 
32;  moisture  in,  135;  sand,  121,  122. 

Solar  system,  217. 

Solution,  292,  302. 

Solvent,  92. 

Sound,  8,  15,  16. 

Specific  gravity,  350,  355. 

Spectrum,  251,  259. 

Speech,  organs  of,  16. 

Spores,  196. 

Stains,  removal  of,  292,  293,  302-05. 

Stamens,  379. 

Standpipe,  82. 

Starch,  145,  148,  153. 

Stars,  216,  217;  north  star,  217;  Great 
Bear,  217. 

Steam,  90;  boiler,  273;  heat,  283;  en- 
gine, 350,  356-58,  361. 

Steamships,  349,  359,  360. 

Stegomyia,  388. 

Sterilization,  66. 

Stigma,  380. 

Stimulant,  180. 

Stones,  for  building,  234. 

Storms,  course  of,  103,  104. 

Stove,  as  a  heater,  279;  draughts  of, 
273;  gas,  274. 

Struggle  for  existence,  375,  384. 


4i6  INDEX 


Stucco,  244. 

Style,  380. 

Submarine,  355. 

Submarine  cables,  333,  339,  344. 

Suction,  12. 

Sugar,  145,  153. 

Sulphur,  25. 

Summer  solstice,  219. 

Sun,  215,  216;  rays  of,  251. 

Superstition,  209. 

Swamps,  137,  138. 

Sweat  glands,  294,  295. 

Switches,  267. 

Tank,  French,  365. 

Tank,  hot-water,  74,  75. 

Tea,  1 80. 

Teeth,  166,  184,  185. 

Telegraph,  333,  336,  339,  343. 

Telegraph  code,  Morse,  336. 

Telephone,  333,  337,  339,  345- 

Temperature,    25,    35,    54;    best    for 

houses,  276. 
Thermometer,  Centigrade,  89, 99, 107; 

Fahrenheit,  89,  99,  107. 
Time,  221. 
Tissue,  44. 

Tobacco,  effects  of,  62,  186,  187. 
Tornado,  3. 
Toxin,  60. 
Trade  winds,  113. 
Transportation,  349-72. 
Tree,  growth  of,  230. 
Trolley-car,  349,  365. 
Tuberculosis,  57,  61,  63,  65. 
Tungsten,  268. 
Tunnels,  17. 
Turbines,  369. 
Typewriter,  347. 
Typhoid  fever,  79,  80,  202,  387. 
Typhoons,  212. 

Vaccination,  386,  387. 
Vacuum,  16;  cleaner,  55. 
Valves,  1 6. 
Variation,  384. 


Veins,  183. 

Ventilation,  51,  54,  55. 
Vitamins,  180. 
Voice,  1 6. 
Volcanoes,  126. 

Washing,  292. 

Washing  machine,  331. 

Waste  matter,  46. 

Water,  68-140;  boiled,  70,  81;  dis- 
tilled, 70,  71,  81;  drinking,  sources 
of,  78;  gauge,  282;  hard,  93;  in  the 
soil,  119,  120;  methods  of  purifying, 
80,  81;  pressure,  82;  pumping  sys- 
tem, 85;  pure  and  impure,  79;  soft, 
78;  supply  systems,  83-85;  table, 
134;  transportation,  352;  wheels, 
369- 

Water  vapor,  in  breathing,  35;  in  the 
air,  26,  54,  55,  98,  105,  108;  steam, 
at  boiling  point,  90. 

Watts,  James,  357. 

Weather,  5,  6,  12,  97;  Bureau,  U.S., 
96,  115;  map/ioi. 

Wedge,  314,  329. 

Weight,  4,  319. 

Wind,  110-13,  289;  action  of,  130; 
causes  of,  100;  storms,  3. 

Windmills,  3,  20. 

Wireless  stations,  333;  telegraph,  340, 
346;  telephone,  346. 

Wood,  as  a  fuel,  275;  as  building  ma- 
terial, 239;  hard  and  soft,  232,  240; 
how  made,  231;  uses  of,  233,  275. 

Wool,  291,  298. 

Work,  317-19;  how  measured,  321. 

Wright,  Wilbur  and  Orville,  19. 

Writing,  338. 

Years,  219. 

Yeast,  196,  198,  199;  temperature 
favorable  for  growth,  191;  carbon 
dioxide  produced  by,  191,  192. 

Yellow  fever,  388. 

Zinc,  255. 


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